Practice Problems

Question 1

01 Matrix
Tech Interview Handbook
https://leetcode.com/problems/01-matrix/description/

Question 2

Imagine a country with several cities. Some cities have direct roads connecting them, while others might be connected through a sequence of intermediary cities. Using a matrix representation, if matrix[i][j] holds the value 1, it indicates that city i is directly linked to city j and vice versa. If it holds 0, then there’s no direct link between them.

Determine the number of separate city clusters (or provinces).

A province is defined as a collection of cities that can be reached from each other either directly or through other cities in the same province.

Examples
Input:
[[1,1,0],[1,1,0],[0,0,1]]
Expected Output:
2
Justification:
There are two provinces: cities 0 and 1 form one province, and city 2 forms its own province.
Input:
[[1,0,0,1],[0,1,1,0],[0,1,1,0],[1,0,0,1]]
Expected Output:
2
Justification:
There are two provinces: cities 0 and 3 are interconnected forming one province, and cities 1 and 2 form another.
Input:
[[1,0,0],[0,1,0],[0,0,1]]
Expected Output:
3
Justification:
Each city stands alone and is not connected to any other city. Thus, we have three provinces.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/651a8380aa7cf9c7c20f9aa8

Question 3

Given an array with positive numbers and a positive target number, find all of its contiguous subarrays whose product is less than the target number.

Example 1:

Input: [2, 5, 3, 10], target=30
Output: [2], [5], [2, 5], [3], [5, 3], [10]
Explanation: There are six contiguous subarrays whose product is less than the target.
Example 2:

Input: [8, 2, 6, 5], target=50
Output: [8], [2], [8, 2], [6], [2, 6], [5], [6, 5]
Explanation: There are seven contiguous subarrays whose product is less than the target.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f976d20f87893374e4e6b

Question 4

Given an array arr of unsorted numbers and a target sum, count all triplets in it such that arr[i] + arr[j] + arr[k] < target where i, j, and k are three different indices. Write a function to return the count of such triplets.

Example 1:

Input: [-1, 0, 2, 3], target=3
Output: 2
Explanation: There are two triplets whose sum is less than the target: [-1, 0, 3], [-1, 0, 2]
Example 2:

Input: [-1, 4, 2, 1, 3], target=5
Output: 4
Explanation: There are four triplets whose sum is less than the target:
[-1, 1, 4], [-1, 1, 3], [-1, 1, 2], [-1, 2, 3]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f7a0a4544c65f117ba260

Question 5

We are given an unsorted array containing ‘n’ numbers taken from the range 1 to ‘n’. The array originally contained all the numbers from 1 to ‘n’, but due to a data error, one of the numbers got duplicated which also resulted in one number going missing. Find both these numbers.

Example 1:

Input: [3, 1, 2, 5, 2]
Output: [2, 4]
Explanation: ‘2’ is duplicated and ‘4’ is missing.
Example 2:

Input: [3, 1, 2, 3, 6, 4]
Output: [3, 5]
Explanation: ‘3’ is duplicated and ‘5’ is missing.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63948b3326086d487e96e4b3

Question 6

Given a 2D array (i.e., a matrix) containing only 1s (land) and 0s (water), find the biggest island in it. Write a function to return the area of the biggest island.

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6388d8940cc1849dcbc27fe3

Question 7

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Example 1:

Input: s = “listen”, t = “silent”
Output: true
Example 2:

Input: s = “rat”, t = “car”
Output: false
Example 3:

Input: s = “hello”, t = “world”
Output: false

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d93a25970f20b6d90eef04

Question 8

Longest Palindrome
Tech Interview Handbook
https://leetcode.com/problems/longest-palindrome/description/

Question 9

Longest Palindromic Substring
Tech Interview Handbook
https://leetcode.com/problems/longest-palindromic-substring/description/

Question 10

Given a string, determine the length of the longest palindrome that can be constructed using the characters from the string. You don’t need to return the palindrome itself, just its maximum possible length.

Examples:

Input: “applepie”
Expected Output: 5
Justification: The longest palindrome that can be constructed from the string is “pepep”, which has a length of 5. There are are other palindromes too but they all will be of length 5.
Input: “aabbcc”
Expected Output: 6
Justification: We can form the palindrome “abccba” using the characters from the string, which has a length of 6.
Input: “bananas”
Expected Output: 5
Justification: The longest palindrome that can be constructed from the string is “anana”, which has a length of 5.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64fd83859592e24ab8b03ab7

Question 11

Add Binary
Tech Interview Handbook
https://leetcode.com/problems/add-binary/description/

Question 12

Given an input array of integers nums, find an integer array, let’s call it differenceArray, of the same length as an input integer array.

Each element of differenceArray, i.e., differenceArray[i], should be calculated as follows: take the sum of all elements to the left of index i in array nums (denoted as leftSum[i]), and subtract it from the sum of all elements to the right of index i in array nums (denoted as rightSum[i]), taking the absolute value of the result. Formally:

differenceArray[i] = | leftSum[i] - rightSum[i] |

If there are no elements to the left/right of i, the corresponding sum should be taken as 0.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651bdef883cd57c6a2fb0ba9

Question 13

Diameter of a Binary Tree
Tech Interview Handbook
https://leetcode.com/problems/diameter-of-binary-tree/description/

Question 14

Given two arrays nums1 and nums2 containing integers only, sorted in increasing order, return the smallest integer that appears in both arrays. If there isn’t any integer that exists in both arrays, the function should return -1.

Examples
Example 1:

input: nums1 = [1, 3, 5, 7], nums2 = [3, 4, 5, 6, 8, 10]
expectedOutput: 3
Justification: Both arrays share the integers 3 and 5, but the smallest common integer is 3.
Example 2:

input: nums1 = [2, 4, 6], nums2 = [1, 3, 5]
expectedOutput: -1
Justification: There are no integers common to both nums1 and nums2, hence the output is -1.
Example 3:

input: nums1 = [1, 2, 2, 3], nums2 = [2, 2, 4]
expectedOutput: 2
Justification: The integer 2 is the only common number between nums1 and nums2, appearing multiple times in both, and it is the smallest.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/663c960668f93bfd45e549a1

Question 15

Given a binary tree, connect each node with its level order successor. The last node of each level should point to a null node.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63989951eb898f72291da2c7

Question 16

Given the head of a Singly LinkedList, write a method to modify the LinkedList such that the nodes from the second half of the LinkedList are inserted alternately to the nodes from the first half in reverse order. So if the LinkedList has nodes 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> null, your method should return 1 -> 6 -> 2 -> 5 -> 3 -> 4 -> null.

Your algorithm should use only constant space the input LinkedList should be modified in-place.

Example 1:

Input: 2 -> 4 -> 6 -> 8 -> 10 -> 12 -> null
Output: 2 -> 12 -> 4 -> 10 -> 6 -> 8 -> null
Example 2:

Input: 2 -> 4 -> 6 -> 8 -> 10 -> null
Output: 2 -> 10 -> 4 -> 8 -> 6 -> null

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63923313ae2ec690ac22b61d

Question 17

Unique Paths
Tech Interview Handbook
https://leetcode.com/problems/unique-paths/description/

Question 18

LRU Cache
Tech Interview Handbook
https://leetcode.com/problems/lru-cache/description/

Question 19

Given two strings containing backspaces (identified by the character ‘#’), check if the two strings are equal.

Example 1:

Input: str1=”xy#z”, str2=”xzz#”
Output: true
Explanation: After applying backspaces the strings become “xz” and “xz” respectively.
Example 2:

Input: str1=”xy#z”, str2=”xyz#”
Output: false
Explanation: After applying backspaces the strings become “xz” and “xy” respectively.
Example 3:

Input: str1=”xp#”, str2=”xyz##”
Output: true
Explanation: After applying backspaces the strings become “x” and “x” respectively.
In “xyz##”, the first ‘#’ removes the character ‘z’ and the second ‘#’ removes the character ‘y’.
Example 4:

Input: str1=”xywrrmp”, str2=”xywrrmu#p”
Output: true
Explanation: After applying backspaces the strings become “xywrrmp” and “xywrrmp” respectively.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638fa28f5844e928cbefff88

Question 20

Determine the depth (or height) of a binary tree, which refers to the number of nodes along the longest path from the root node to the farthest leaf node. If the tree is empty, the depth is 0.

Example:

Input
1
/ \
2 3
/ \
4 5
Output: 3
Explanation: The longest path is 1->2->4 or 1->2->5 with 3 nodes.

Input:
1
\
2
\
3
Expected Output: 3
Justification: There’s only one path 1->2->3 with 3 nodes.
Input:
1
/ \
2 3
/ \
4 7
\
9
Expected Output: 4
Justification: The longest path is 1->2->7->9 with 4 nodes.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f22febde9e448f5e3f653d

Question 21

Word Search
Tech Interview Handbook
https://leetcode.com/problems/word-search/description/

Question 22

Given a binary tree and a number ‘S’, find all paths from root-to-leaf such that the sum of all the node values of each path equals ‘S’.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6399d2d989924acc4bea0939

Question 23

Given a binary tree, populate an array to represent its zigzag level order traversal. You should populate the values of all nodes of the first level from left to right, then right to left for the next level and keep alternating in the same manner for the following levels.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63979996c8fbc9fe77f1feb0

Question 24

Lowest Common Ancestor of a Binary Tree
Tech Interview Handbook
https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/

Question 25

Given an undirected graph, represented as a list of edges. Each edge is illustrated as a pair of integers [u, v], signifying that there’s a mutual connection between node u and node v.

Given this graph, a starting node start, and a destination node end, your task is to ascertain if a path exists between the starting node and the destination node.

Examples
Example 1:

Input: 4, [[0,1],[1,2],[2,3]], 0, 3
Expected Output: true
Justification: There’s a path from node 0 -> 1 -> 2 -> 3.
Example 2:

Input: 4, [[0,1],[2,3]], 0, 3
Expected Output: false
Justification: Nodes 0 and 3 are not connected, so no path exists between them.
Example 3:

Input: 5, [[0,1],[3,4]], 0, 4
Expected Output: false
Justification: Nodes 0 and 4 are not connected in any manner.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/651a80b8f0749a59d1e0228d

Question 26

Time Based Key-Value Store
Tech Interview Handbook
https://leetcode.com/problems/time-based-key-value-store/description/

Question 27

Evaluate Reverse Polish Notation
Tech Interview Handbook
https://leetcode.com/problems/evaluate-reverse-polish-notation/

Question 28

Given a binary tree and a number sequence, find if the sequence is present as a root-to-leaf path in the given tree.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6399dbf40d7254be596612d2

Question 29

Given a stack, sort it using only stack operations (push and pop).

You can use an additional temporary stack, but you may not copy the elements into any other data structure (such as an array). The values in the stack are to be sorted in descending order, with the largest elements on top.

Examples
1. Input: [34, 3, 31, 98, 92, 23]
Output: [3, 23, 31, 34, 92, 98]

2. Input: [4, 3, 2, 10, 12, 1, 5, 6]
   Output: [1, 2, 3, 4, 5, 6, 10, 12]
3. Input: [20, 10, -5, -1]
   Output: [-5, -1, 10, 20]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64902bd715f14528a3ef7363

Question 30

Given an array of strings words and two different strings that already exist in the array word1 and word2, return the shortest distance between these two words in the list.

Example 1:

Input: words = [“the”, “quick”, “brown”, “fox”, “jumps”, “over”, “the”, “lazy”, “dog”], word1 = “fox”, word2 = “dog”
Output: 5
Explanation: The distance between “fox” and “dog” is 5 words.
Example 2:

Input: words = [“a”, “c”, “d”, “b”, “a”], word1 = “a”, word2 = “b”
Output: 1
Explanation: The shortest distance between “a” and “b” is 1 word. Please note that “a” appeared twice.
Example 3:

Input: words = [“a”, “b”, “c”, “d”, “e”], word1 = “a”, word2 = “e”
Output: 4
Explanation: The distance between “a” and “e” is 4 words.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63daaa1a0d01fe363b68c8d4

Question 31

Given a root node of the Binary Search Tree (BST) and integer ‘k’. Return the Kth smallest element among all node values of the binary tree.

Examples:

Example 1:
Input:

8    / \   3   10  / \    \ 1   6    14    /  \  /   4   7  13 k = 4 Expected Output: 6 Justification: The in-order traversal of the tree is [1, 3, 4, 6, 7, 8, 10, 13, 14]. The 4th element in this sequence is 6.

Example 2:
Input:

5    / \   2   6  / 1 k = 3 Expected Output: 5 Justification: The in-order traversal of the tree is [1, 2, 5, 6]. The 3rd element in this sequence is 5.

Example 3:
Input:

1
\
3
/
2
k = 2
Expected Output: 2
Justification: The in-order traversal of the tree is [1, 2, 3]. The 2nd element in this sequence is 2.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f2c4a66a55d05df40e019d

Question 32

Lowest Common Ancestor of a Binary Search Tree
Tech Interview Handbook
https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/

Question 33

We are given an array containing n objects. Each object, when created, was assigned a unique number from the range 1 to n based on their creation sequence. This means that the object with sequence number 3 was created just before the object with sequence number 4.

Write a function to sort the objects in-place on their creation sequence number in without using any extra space. For simplicity, let’s assume we are passed an integer array containing only the sequence numbers, though each number is actually an object.

Example 1:

Input: [3, 1, 5, 4, 2]
Output: [1, 2, 3, 4, 5]
Example 2:

Input: [2, 6, 4, 3, 1, 5]
Output: [1, 2, 3, 4, 5, 6]
Example 3:

Input: [1, 5, 6, 4, 3, 2]
Output: [1, 2, 3, 4, 5, 6]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6393a98bd8a93f4bff961b4d

Question 34

Given a binary tree, connect each node with its level order successor. The last node of each level should point to the first node of the next level.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63989c048d812da0aa12bff7

Question 35

Implement Trie (Prefix Tree)
Tech Interview Handbook
https://leetcode.com/problems/implement-trie-prefix-tree/description/

Question 36

Climbing Stairs
Tech Interview Handbook
https://leetcode.com/problems/climbing-stairs/description/

Question 37

Given divisor1, divisor2, uniqueCnt1, and uniqueCnt2 integers, find the smallest possible maximum integer that could be present in either array after they are filled according to the below conditions.

You can take two arrays arr1 and arr2 which are initially empty.
arr1 contains total uniqueCnt1 different positive integers, each of them is not divisible by divisor1.
arr2 contains total uniqueCnt2 different positive integers, each of them is divisible by divisor2.
There are no common integers in both arrays.
Examples
Example 1:

Input: uniqueCnt1 = 2, divisor1 = 2, uniqueCnt2 = 2, divisor2 = 3
Expected Output: 4
Explanation: The optimal arrays could be arr1 = [1, 3] (numbers not divisible by 2) and arr2 = [2, 4] (numbers not divisible by 3). The maximum number among both arrays is 4.
Example 2:

Input: uniqueCnt1 = 3, divisor1 = 3, uniqueCnt2 = 4, divisor2 = 4
Expected Output: 7
Explanation: Possible arrays are arr1 = [1, 2, 4] and arr2 = [3, 5, 6, 7]. The highest integer used is 7.
Example 3:

Input: uniqueCnt1 = 1, divisor1 = 7, uniqueCnt2 = 1, divisor2 = 10
Expected Output: 2
Explanation: We can use arr1 = [1] (since it’s not divisible by 7) and arr2 = [2] (since it’s not divisible by 10). The highest integer here is 2.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/663cbbbd0f27fd5b0be90e83

Question 38

We are given an array containing n distinct numbers taken from the range 0 to n. Since the array has only n numbers out of the total n+1 numbers, find the missing number.

Example 1:

Input: [4, 0, 3, 1]
Output: 2
Example 2:

Input: [8, 3, 5, 2, 4, 6, 0, 1]
Output: 7

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6393ab5cd8a93f4bff961bc7

Question 39

Container with Most Water
Tech Interview Handbook
https://leetcode.com/problems/container-with-most-water/description/

Question 40

Find All Anagrams in a String
Tech Interview Handbook
https://leetcode.com/problems/find-all-anagrams-in-a-string/description/

Question 41

Given a binary tree, populate an array to represent its level-by-level traversal in reverse order, i.e., the lowest level comes first. You should populate the values of all nodes in each level from left to right in separate sub-arrays.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6397900a721fdbdbc77e92ad

Question 42

Permutations
Tech Interview Handbook
https://leetcode.com/problems/permutations/description/

Question 43

Flood Fill
Tech Interview Handbook
https://leetcode.com/problems/flood-fill/description/

Question 44

Given two lists of intervals, find the intersection of these two lists. Each list consists of disjoint intervals sorted on their start time.

Example 1:

Input: arr1=[[1, 3], [5, 6], [7, 9]], arr2=[[2, 3], [5, 7]]
Output: [2, 3], [5, 6], [7, 7]
Explanation: The output list contains the common intervals between the two lists.
Example 2:

Input: arr1=[[1, 3], [5, 7], [9, 12]], arr2=[[5, 10]]
Output: [5, 7], [9, 10]
Explanation: The output list contains the common intervals between the two lists.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639249470cddc1617da1b889

Question 45

We are given an unsorted array containing numbers taken from the range 1 to ‘n’. The array can have duplicates, which means some numbers will be missing. Find all those missing numbers.

Example 1:

Input: [2, 3, 1, 8, 2, 3, 5, 1]
Output: 4, 6, 7
Explanation: The array should have all numbers from 1 to 8, due to duplicates 4, 6, and 7 are missing.
Example 2:

Input: [2, 4, 1, 2]
Output: 3
Example 3:

Input: [2, 3, 2, 1]
Output: 4

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6393ada834689e585e94a1b9

Question 46

Invert Binary Tree
Tech Interview Handbook
https://leetcode.com/problems/invert-binary-tree/description/

Question 47

Given an absolute file path in a Unix-style file system, simplify it by converting “..” to the previous directory and removing any “.” or multiple slashes. The resulting string should represent the shortest absolute path.

Examples:
1.
Input: “/a//b////c/d//././/..”
Output: “/a/b/c”

2. Input: “/../”
   Output: “/”
3. Input: “/home//foo/”
   Output: “/home/foo”

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64902fec5d0034e2d16110aa

Question 48

Given an array of sorted numbers, move all non-duplicate number instances at the beginning of the array in-place. The non-duplicate numbers should be sorted and you should not use any extra space so that the solution has constant space complexity i.e., .

Move all the unique number instances at the beginning of the array and after moving return the length of the subarray that has no duplicate in it.

Example 1:

Input: [2, 3, 3, 3, 6, 9, 9]
Output: 4
Explanation: The first four elements after moving element will be [2, 3, 6, 9].
Example 2:

Input: [2, 2, 2, 11]
Output: 2
Explanation: The first two elements after moving elements will be [2, 11].

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638e33feac0cc8a9358a25ac

Question 49

Combination Sum
Tech Interview Handbook
https://leetcode.com/problems/combination-sum/description/

Question 50

Given a string, determine the maximum number of times the word “balloon” can be formed using the characters from the string. Each character in the string can be used only once.

Examples:

Example 1:

Input: “balloonballoon”
Expected Output: 2
Justification: The word “balloon” can be formed twice from the given string.
Example 2:

Input: “bbaall”
Expected Output: 0
Justification: The word “balloon” cannot be formed from the given string as we are missing the character ‘o’ twice.
Example 3:

Input: “balloonballoooon”
Expected Output: 2
Justification: The word “balloon” can be formed twice, even though there are extra ‘o’ characters.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64fd60b82322f34a81703611

Question 51

First Bad Version
Tech Interview Handbook
https://leetcode.com/problems/first-bad-version/description/

Question 52

Given a binary search tree (BST) and a target number, you need to find a node value in the BST that is closest to the given target. A BST is a tree where for every node, the values in the left subtree are smaller than the node, and the values in the right subtree are greater.

Examples:

Example 1:

Input:

Tree: 
   5
 /   \
3     8    / \   / \   1   4 6   9 Target: 6.4

Expected Output: 6

Justification: The values 6 and 8 are the closest numbers to 6.4 in the tree. Among them, 6 is closer.

Example 2:

Input:

Tree:
   20
 /    \
10     30 Target: 25

Expected Output: 20

Justification: 20 and 30 are the closest numbers to 25. However, 20 is closer than 30.

Example 3:

Input:

Tree:
   2
 /   \
1     3 Target: 2.9

Expected Output: 3

Justification: 3 is the closest value to 2.9 in the tree.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f2ccca6a55d05df40e51b2

Question 53

Given a binary tree and a number ‘S’, find all paths in the tree such that the sum of all the node values of each path equals ‘S’. Please note that the paths can start or end at any node but all paths must follow direction from parent to child (top to bottom).

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6399e360a0e842698079404f

Question 54

Accounts Merge
Tech Interview Handbook
https://leetcode.com/problems/accounts-merge/description/

Question 55

Valid Anagram
Tech Interview Handbook
https://leetcode.com/problems/valid-anagram/description/

Question 56

A bike rider is going on a ride. The road contains n + 1 points at different altitudes. The rider starts from point 0 at an altitude of 0.

Given an array of integers gain of length n, where gain[i] represents the net gain in altitude between points i and i + 1 for all (0 <= i < n), return the highest altitude of a point.

Examples
Example 1
Input: gain = [-5, 1, 5, 0, -7]
Expected Output: 1
Justification: The altitude changes are [-5, -4, 1, 1, -6], where 1 is the highest altitude reached.
Example 2
Input: gain = [4, -3, 2, -1, -2]
Expected Output: 4
Justification: The altitude changes are [4, 1, 3, 2, 0], where 4 is the highest altitude reached.
Example 3
Input: gain = [2, 2, -3, -1, 2, 1, -5]
Expected Output: 4
Justification: The altitude changes are [2, 4, 1, 0, 2, 3, -2], where 4 is the highest altitude reached.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651be1c083cd57c6a2fb1542

Question 57

Find the minimum depth of a binary tree. The minimum depth is the number of nodes along the shortest path from the root node to the nearest leaf node.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6397ac3f197fbea348eb0f04

Question 58

Given an array containing 0s, 1s and 2s, sort the array in-place. You should treat numbers of the array as objects, hence, we can’t count 0s, 1s, and 2s to recreate the array.

The flag of the Netherlands consists of three colors: red, white and blue; and since our input array also consists of three different numbers that is why it is called Dutch National Flag problem.

Example 1:

Input: [1, 0, 2, 1, 0]
Output: [0 0 1 1 2]
Example 2:

Input: [2, 2, 0, 1, 2, 0]
Output: [0 0 1 2 2 2 ]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f9b3e239cfbfb10ee82f3

Question 59

Given a binary matrix that has dimensions , consisting of ones and zeros, determine the row that contains the highest number of ones and return two values: the zero-based index of this row and the actual count of ones it possesses.

If there is a tie, i.e., multiple rows contain the same maximum number of ones, we must select the row with the lowest index.

Examples
Example 1:

Input: [[1, 0], [1, 1], [0, 1]]
Expected Output: [1, 2]
Justification: The second row [1, 1] contains the most ones, so the output is [1, 2].
Example 2:

Input: [[0, 1, 1], [0, 1, 1], [1, 1, 1]]
Expected Output: [2, 3]
Justification: The third row [1, 1, 1] has the most ones, leading to the output [2, 3].
Example 3:

Input: [[1, 0, 1], [0, 0, 1], [1, 1, 0]]
Expected Output: [0, 2]
Justification: Both the first and third rows contain two ones, but we choose the first due to its lower index, resulting in [0, 2].

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651bbf379aa5328fe5ae4983

Question 60

Task Scheduler
Tech Interview Handbook
https://leetcode.com/problems/task-scheduler/description/

Question 61

HARD

We are given an array containing positive and negative numbers. Suppose the array contains a number ‘M’ at a particular index. Now, if ‘M’ is positive we will move forward ‘M’ indices and if ‘M’ is negative move backwards ‘M’ indices. You should assume that the array is circular which means two things:

If, while moving forward, we reach the end of the array, we will jump to the first element to continue the movement.
If, while moving backward, we reach the beginning of the array, we will jump to the last element to continue the movement.
Write a method to determine if the array has a cycle. The cycle should have more than one element and should follow one direction which means the cycle should not contain both forward and backward movements.

Example 1:

Input: [1, 2, -1, 2, 2]
Output: true
Explanation: The array has a cycle among indices: 0 -> 1 -> 3 -> 0
Example 2:

Input: [2, 2, -1, 2]
Output: true
Explanation: The array has a cycle among indices: 1 -> 3 -> 1
Example 3:

Input: [2, 1, -1, -2]
Output: false
Explanation: The array does not have any cycle.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6392394ee4cb724ea7189954

Question 62

Given two binary trees, root1 and root2, merge them into a single, new binary tree.

If two nodes from the given trees share the same position, their values should be summed up in the resulting tree. If a node exists in one tree but not in the other, the resulting tree should have a node at the same position with the value from the existing node.

Examples

Example 1:

Trees:

Tree 1: 1 Tree 2: 1
/ \ / \
3 2 2 3

Merged: 2
/ \
5 5
Justification: The root nodes of both trees have the value 1, so the merged tree’s root has a value of 1 + 1 = 2. For the left child, 3 + 2 = 5 and for the right child, 2 + 3 = 5.

Example 2:

Trees:

Tree 1: 5 Tree 2: 3
/ \ / \
4 7 2 6

Merged: 8
/ \
6 13
Justification: The root nodes have values 5 and 3 respectively. So, the merged tree’s root value becomes 5 + 3 = 8. The left child is 4 + 2 = 6 and the right child is 7 + 6 = 13.

Example 3:

Trees:

Tree 1: 2 Tree 2: 2
\ /
5 3

Merged: 4
/ \
3 5
Justification: The root nodes have values 2 each, so the merged tree’s root value is 2 + 2 = 4. Tree 1 doesn’t have a left child, so we take the left child of Tree 2 as it is, which is 3. Similarly, Tree 2 doesn’t have a right child, so the merged tree’s right child is the same as Tree 1, which is 5.

Example 4:

Trees:

Tree 1: 10 Tree 2: 10
/ \ / \
5 15 6 16

Merged: 20
/ \
11 31
Justification: The root nodes have the value 10, so they add up to 20 for the merged tree. The left child values add up to 5 + 6 = 11 and the right child values sum up to 15 + 16 = 31.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f2d12d9654890c5a9ab5ef

Question 63

Validate Binary Search Tree
Tech Interview Handbook
https://leetcode.com/problems/validate-binary-search-tree/description/

Question 64

Best Time to Buy and Sell Stock
Tech Interview Handbook
https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/

Question 65

We are given an unsorted array containing n+1 numbers taken from the range 1 to n. The array has only one duplicate but it can be repeated multiple times. Find that duplicate number without using any extra space. You are, however, allowed to modify the input array.

Example 1:

Input: [1, 4, 4, 3, 2]
Output: 4
Example 2:

Input: [2, 1, 3, 3, 5, 4]
Output: 3
Example 3:

Input: [2, 4, 1, 4, 4]
Output: 4

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6393aee5ba7c985340679287

Question 66

Given a list of intervals, merge all the overlapping intervals to produce a list that has only mutually exclusive intervals.

Example 1:

Intervals: [[1,4], [2,5], [7,9]]
Output: [[1,5], [7,9]]
Explanation: Since the first two intervals [1,4] and [2,5] overlap, we merged them into one [1,5].

Example 2:

Intervals: [[6,7], [2,4], [5,9]]
Output: [[2,4], [5,9]]
Explanation: Since the intervals [6,7] and [5,9] overlap, we merged them into one [5,9].
Example 3:

Intervals: [[1,4], [2,6], [3,5]]
Output: [[1,6]]
Explanation: Since all the given intervals overlap, we merged them into one.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63923e6de4cb724ea719007a

Question 67

Valid Parentheses
Tech Interview Handbook
https://leetcode.com/problems/valid-parentheses/description/

Question 68

Given the head of a Singly LinkedList, write a function to determine if the LinkedList has a cycle in it or not.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639105492e1c0a1cfe6c1eb9

Question 69

Rotting Oranges
Tech Interview Handbook
https://leetcode.com/problems/rotting-oranges/description/

Question 70

Given a list of integers, determine the count of numbers for which there exists another number in the list that is greater by exactly one unit.

In other words, for each number x in the list, if x + 1 also exists in the list, then x is considered for the count.

Examples:

Example 1:

Input: [4, 3, 1, 5, 6]
Expected Output: 3
Justification: The numbers 4, 3, and 5 have 5, 4, and 6 respectively in the list, which are greater by exactly one unit.
Example 2:

Input: [7, 8, 9, 10]
Expected Output: 3
Justification: The numbers 7, 8, and 9 have 8, 9, and 10 respectively in the list, which are greater by exactly one unit.
Example 3:

Input: [11, 13, 15, 16]
Expected Output: 1
Justification: Only the number 15 has 16 in the list, which is greater by exactly one unit.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64fd596617ec3ee5197634f4

Question 71

Given an array of integers nums, return the number of good pairs.

A pair (i, j) is called good if nums[i] == nums[j] and i < j.

Example 1:

Input: nums = [1,2,3,1,1,3]
Output: 4
Explanation: There are 4 good pairs, here are the indices: (0,3), (0,4), (3,4), (2,5).
Example 2:

Input: nums = [1,1,1,1]
Output: 6
Explanation: Each pair in the array is a ‘good pair’.
Example 3:

Input: words = nums = [1,2,3]
Output: 0
Explanation: No number is repeating.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63dac2b3bbc58b880202c251

Question 72

Given a string, write a function that uses a stack to reverse the string. The function should return the reversed string.

Examples
Example 1:

Input: “Hello, World!”
Output: “!dlroW ,olleH”
Example 2:

Input: “OpenAI”
Output: “IAnepO”
Example 3:

Input: “Stacks are fun!”
Output: “!nuf era skcatS”

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6490189d822978cc90e2ace0

Question 73

Clone Graph
Tech Interview Handbook
https://leetcode.com/problems/clone-graph/description/

Question 74

Given a doubly linked list, determine whether it is a palindrome.

A doubly linked list is a palindrome if it reads the same backward as forward, utilizing the previous and next pointers of the nodes.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/65101ae0919cfcaef3156b95

Question 75

Given a binary tree and a number ‘S’, find if the tree has a path from root-to-leaf such that the sum of all the node values of that path equals ‘S’.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6398a0a974c44bdc88129966

Question 76

Number of Islands
Tech Interview Handbook
https://leetcode.com/problems/number-of-islands/description/

Question 77

Given a one-dimensional array of integers, create a new array that represents the running sum of the original array.

The running sum at position i in the new array is calculated as the sum of all the numbers in the original array from the 0th index up to the i-th index (inclusive). Formally, the resulting array should be computed as follows: result[i] = sum(nums[0] + nums[1] + … + nums[i]) for each i from 0 to the length of the array minus one.

Examples
Example 1

Input: [2, 3, 5, 1, 6]
Expected Output: [2, 5, 10, 11, 17]
Justification:
For i=0: 2
For i=1: 2 + 3 = 5
For i=2: 2 + 3 + 5 = 10
For i=3: 2 + 3 + 5 + 1 = 11
For i=4: 2 + 3 + 5 + 1 + 6 = 17
Example 2

Input: [1, 1, 1, 1, 1]
Expected Output: [1, 2, 3, 4, 5]
Justification: Each element is simply the sum of all preceding elements plus the current element.
Example 3

Input: [-1, 2, -3, 4, -5]
Expected Output: [-1, 1, -2, 2, -3]
Justification: Negative numbers are also summed up in the same manner as positive ones.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651bdcbb5a884f25a9c00863

Question 78

Balanced Binary Tree
Tech Interview Handbook
https://leetcode.com/problems/balanced-binary-tree/description/

Question 79

Kth Smallest Element in a BST
Tech Interview Handbook
https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/

Question 80

Search in Rotated Sorted Array
Tech Interview Handbook
https://leetcode.com/problems/search-in-rotated-sorted-array/description/

Question 81

Given a positive integer n, write a function that returns its binary equivalent as a string. The function should not use any in-built binary conversion function.

Examples
Example 1:

Input: 2
Output: “10”
Explanation: The binary equivalent of 2 is 10.
Example 2:

Input: 7
Output: “111”
Explanation: The binary equivalent of 7 is 111.
Example 3:

Input: 18
Output: “10010”
Explanation: The binary equivalent of 18 is 10010.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6490145d2d3ff689ba978d02

Question 82

Course Schedule
Tech Interview Handbook
https://leetcode.com/problems/course-schedule/description/

Question 83

You are given an m x n matrix accounts where accounts[i][j] is the amount of money the i​​​​​​​​​​​th​​​​ customer has in the j​​​​​​​​​​​th​​​​ bank.

Return the wealth that the richest customer has.

Imagine every customer has multiple bank accounts, with each account holding a certain amount of money. The total wealth of a customer is calculated by summing all the money across all their multiple.

Examples
Example 1:

Input: [[5,2,3],[0,6,7]]
Expected Output: 13
Justification: The total wealth of the first customer is 10 and of the second customer is 13. So, the output is 13 as it’s the maximum among all customers.
Example 2:

Input: [[1,2],[3,4],[5,6]]
Expected Output: 11
Justification: Total wealth for each customer is [3, 7, 11]. Maximum of these is 11.
Example 3:

Input: [[10,100],[200,20],[30,300]]
Expected Output: 330
Justification: Total wealth for each customer is [110, 220, 330]. The wealthiest customer has 330.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651bba625b23f17e05299274

Question 84

Given an array of unsorted numbers and a target number, find all unique quadruplets in it, whose sum is equal to the target number.

Example 1:

Input: [4, 1, 2, -1, 1, -3], target=1
Output: [-3, -1, 1, 4], [-3, 1, 1, 2]
Explanation: Both the quadruplets add up to the target.
Example 2:

Input: [2, 0, -1, 1, -2, 2], target=2
Output: [-2, 0, 2, 2], [-1, 0, 1, 2]
Explanation: Both the quadruplets add up to the target.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f9cab70b3327d7a210d9d

Question 85

You are given a 2D matrix containing only 1s (land) and 0s (water).

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

Two islands are considered the same if and only if they can be translated (not rotated or reflected) to equal each other.

Write a function to find the number of distinct islands in the given matrix.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638c920fa19edaace544c805

Question 86

Given two strings. The first string represents types of jewels, where each character is a unique type of jewel. The second string represents stones you have, where each character represents a type of stone. Determine how many of the stones you have are also jewels.

Examples:

Example 1:

Input: Jewels = “abc”, Stones = “aabbcc”
Expected Output: 6
Justification: All the stones are jewels.
Example 2:

Input: Jewels = “aA”, Stones = “aAaZz”
Expected Output: 3
Justification: There are 2 ‘a’ and 1 ‘A’ stones that are jewels.
Example 3:

Input: Jewels = “zZ”, Stones = “zZzZzZ”
Expected Output: 6
Justification: All the stones are jewels.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64fd6e571dcab5beab2127d1

Question 87

Middle of the Linked List
Tech Interview Handbook
https://leetcode.com/problems/middle-of-the-linked-list/description/

Question 88

Given a binary tree, find the length of its diameter. The diameter of a tree is the number of nodes on the longest path between any two leaf nodes. The diameter of a tree may or may not pass through the root.

Note: You can always assume that there are at least two leaf nodes in the given tree.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639b62040dbaa5118a4b5e96

Question 89

Binary Tree Level Order Traversal
Tech Interview Handbook
https://leetcode.com/problems/binary-tree-level-order-traversal/description/

Question 90

You are given a 2D matrix containing only 1s (land) and 0s (water).

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

There are no lakes on the island, so the water inside the island is not connected to the water around it. A cell is a square with a side length of 1..

The given matrix has only one island, write a function to find the perimeter of that island.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638c857a34bb69a286c79f30

Question 91

You are given an nums array containing n integers and an integer k. In a single operation, you can choose any index i and increment the nums[i] by 1.

Return the maximum possible frequency of any element of nums after performing at most k operations.

Examples
Example 1:

Input: nums = [1, 2, 3], k = 3
Expected Output: 3
Explanation: We can increment the number 1 two times and 2 one time. The final array will be [3, 3, 3]. Now, the number 3 appears 3 times in the array [3, 3, 3].
Example 2:

Input: nums = [4, 4, 4, 1], k = 2
Expected Output: 3
Explanation: We can increment the number 1 two times (1 -> 2 -> 3). Now, the number 4 still appears 3 times, which is the maximum frequency that can be achieved with 2 operations.
Example 3:

Input: nums = [10, 9, 9, 4, 8], k = 5
Expected Output: 4
Explanation: We can increment the number 9 one time and the number 8 two times (9 -> 10, 9 -> 10; 8 -> 9 -> 10). The number 10 will then appear 4 times in the array [10, 10, 10, 4, 10].

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/663caa3b68f93bfd45e64bbe

Question 92

Given the head of a Singly LinkedList, write a method to return the middle node of the LinkedList.

If the total number of nodes in the LinkedList is even, return the second middle node.

Example 1:

Input: 1 -> 2 -> 3 -> 4 -> 5 -> null
Output: 3
Example 2:

Input: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> null
Output: 4
Example 3:

Input: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> null
Output: 4

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63922bb1b689b698075a9a59

Question 93

Given the head of a Singly LinkedList that contains a cycle, write a function to find the starting node of the cycle.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6391094ea637a0a5c98582ee

Question 94

Given an array of unsorted numbers and a target number, find a triplet in the array whose sum is as close to the target number as possible, return the sum of the triplet. If there are more than one such triplet, return the sum of the triplet with the smallest sum.

Example 1:

Input: [-1, 0, 2, 3], target=3
Output: 2
Explanation: The triplet [-1, 0, 3] has the sum ‘2’ which is closest to the target.

There are two triplets with distance ‘1’ from the target: [-1, 0, 3] & [-1, 2, 3]. Between these two triplets, the correct answer will be [-1, 0, 3] as it has a sum ‘2’ which is less than the sum of the other triplet which is ‘4’. This is because of the following requirement: ‘If there are more than one such triplet, return the sum of the triplet with the smallest sum.’
Example 2:

Input: [-3, -1, 1, 2], target=1
Output: 0
Explanation: The triplet [-3, 1, 2] has the closest sum to the target.
Example 3:

Input: [1, 0, 1, 1], target=100
Output: 3
Explanation: The triplet [1, 1, 1] has the closest sum to the target.
Example 4:

Input: [0, 0, 1, 1, 2, 6], target=5
Output: 4
Explanation: There are two triplets with distance ‘1’ from target: [1, 1, 2] & [0, 0, 6]. Between these two triplets, the correct answer will be [1, 1, 2] as it has a sum ‘4’ which is less than the sum of the other triplet which is ‘6’. This is because of the following requirement: ‘If there are more than one such triplet, return the sum of the triplet with the smallest sum.’

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f7323ae53511bdc364dab

Question 95

Binary Tree Right Side View
Tech Interview Handbook
https://leetcode.com/problems/binary-tree-right-side-view/description/

Question 96

Implement Queue using Stacks
Tech Interview Handbook
https://leetcode.com/problems/implement-queue-using-stacks/description/

Question 97

Given a Binary Search Tree (BST) and a range defined by two integers, L and R, calculate the sum of all the values of nodes that fall within this range. The node’s value is inclusive within the range if and only if L <= node’s value <= R.

Examples:

Example 1:

Input:

Tree:
10
/ \
5 15
/ \ \
3 7 18
Range: [7, 15]
Expected Output: 32

Justification: The values that fall within the range [7, 15] are 7, 10, and 15. Their sum is 7 + 10 + 15 = 32.

Example 2:

Input:

Tree:
20
/ \
5 25
/ \
3 10
Range: [3, 10]
Expected Output: 18

Justification: The values within the range [3, 10] are 3, 5, and 10. Their sum is 3 + 5 + 10 = 18.

Example 3:

Input:

Tree:
30
\
35
/
32
Range: [30, 34]
Expected Output: 62

Justification: The values within the range [30, 34] are 30 and 32. Their sum is 30 + 32 = 62.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f2c93d6a55d05df40e28c2

Question 98

Given an array, find the length of the smallest subarray in it which when sorted will sort the whole array.

Example 1:

Input: [1, 2, 5, 3, 7, 10, 9, 12]
Output: 5
Explanation: We need to sort only the subarray [5, 3, 7, 10, 9] to make the whole array sorted
Example 2:

Input: [1, 3, 2, 0, -1, 7, 10]
Output: 5
Explanation: We need to sort only the subarray [1, 3, 2, 0, -1] to make the whole array sorted
Example 3:

Input: [1, 2, 3]
Output: 0
Explanation: The array is already sorted
Example 4:

Input: [3, 2, 1]
Output: 3
Explanation: The whole array needs to be sorted.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638fa5205844e928cbf004bf

Question 99

Given a string s, where * represents a star. We can remove a star along with its closest non-star character to its left in a single operation.

The task is to perform as many such operations as possible until all stars have been removed and return the resultant string.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64903dd726f49aa43e0b32cb

Question 100

Given a binary tree, populate an array to represent the averages of all of its levels.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6397aabd009f4ccc0648b8ca

Question 101

Longest Substring w/o Repeating Characters
Tech Interview Handbook
https://leetcode.com/problems/longest-substring-without-repeating-characters/description/

Question 102

Given a binary tree where each node can only have a digit (0-9) value, each root-to-leaf path will represent a number. Find the total sum of all the numbers represented by all paths.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6399d8d20d7254be596610f4

Question 103

Given two strings, one representing a ransom note and the other representing the available letters from a magazine, determine if it’s possible to construct the ransom note using only the letters from the magazine. Each letter from the magazine can be used only once.

Examples:

Example 1:

Input: Ransom Note = “hello”, Magazine = “hellworld”
Expected Output: true
Justification: The word “hello” can be constructed from the letters in “hellworld”.
Example 2:

Input: Ransom Note = “notes”, Magazine = “stoned”
Expected Output: true
Justification: The word “notes” can be fully constructed from “stoned” from its first 5 letters.
Example 3:

Input: Ransom Note = “apple”, Magazine = “pale”
Expected Output: false
Justification: The word “apple” cannot be constructed from “pale” as we are missing one ‘p’.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64fd6a77826e0e8c47b7f345

Question 104

Given the head of a Singly LinkedList, write a method to check if the LinkedList is a palindrome or not.

Your algorithm should use constant space and the input LinkedList should be in the original form once the algorithm is finished. The algorithm should have O(N) time complexity where ‘N’ is the number of nodes in the LinkedList.

Example 1:

Input: 2 -> 4 -> 6 -> 4 -> 2 -> null
Output: true
Example 2:

Input: 2 -> 4 -> 6 -> 4 -> 2 -> 2 -> null
Output: false

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63922d27b689b698075a9ab3

Question 105

Contains Duplicate
Tech Interview Handbook
https://leetcode.com/problems/contains-duplicate/description/

Question 106

Linked List Cycle
Tech Interview Handbook
https://leetcode.com/problems/linked-list-cycle/description/

Question 107

Given an array of integers, determine if the number of times each distinct integer appears in the array is unique.

In other words, the occurrences of each integer in the array should be distinct from the occurrences of every other integer.

Examples:

Input: [4, 5, 4, 6, 6, 6]
Expected Output: true
Justification: The number 4 appears 2 times, 5 appears 1 time, and 6 appears 3 times. All these occurrences (1, 2, 3) are unique.
Input: [7, 8, 8, 9, 9, 9, 10, 10]
Expected Output: false
Justification: The number 7 appears 1 time, 8 appears 2 times, 9 appears 3 times, and 10 appears 2 times. The occurrences are not unique since the number 2 appears twice.
Input: [11, 12, 13, 14, 14, 15, 15, 15]
Expected Output: false
Justification: The number 11 appears 1 time, 12 appears 1 time, 13 appears 1 time, 14 appears 2 times, and 15 appears 3 times. These occurrences are not unique.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64fd7aeb75e03702eeb2c23e

Question 108

String to Integer (atoi)
Tech Interview Handbook
https://leetcode.com/problems/string-to-integer-atoi/description/

Question 109

Subsets
Tech Interview Handbook
https://leetcode.com/problems/subsets/description/

Question 110

Reverse Linked List
Tech Interview Handbook
https://leetcode.com/problems/majority-element/description/

Question 111

Given an array of positive integers and a number ‘S,’ find the length of the smallest contiguous subarray whose sum is greater than or equal to ‘S’. Return 0 if no such subarray exists.

Example 1:

Input: [2, 1, 5, 2, 3, 2], S=7
Output: 2
Explanation: The smallest subarray with a sum greater than or equal to ‘7’ is [5, 2].
Example 2:

Input: [2, 1, 5, 2, 8], S=7
Output: 1
Explanation: The smallest subarray with a sum greater than or equal to ‘7’ is [8].
Example 3:

Input: [3, 4, 1, 1, 6], S=8
Output: 3
Explanation: Smallest subarrays with a sum greater than or equal to ‘8’ are [3, 4, 1] or [1, 1, 6].

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/636b1d083b22faa3e89b2478

Question 112

Given a string s containing (, ), [, ], {, and } characters. Determine if a given string of parentheses is balanced.

A string of parentheses is considered balanced if every opening parenthesis has a corresponding closing parenthesis in the correct order.

Example 1:

Input: String s = “{[()]}”;
Expected Output: true
Explanation: The parentheses in this string are perfectly balanced. Every opening parenthesis ‘{‘, ‘[’, ‘(‘ has a corresponding closing parenthesis ‘}’, ‘]’, ‘)’ in the correct order.

Example 2:

Input: string s = “{[}]”;
Expected Output: false
Explanation: The brackets are not balanced in this string. Although it contains the same number of opening and closing brackets for each type, they are not correctly ordered. The ‘]’ closes ‘[’ before ‘{‘ can be closed by ‘}’, and similarly, ‘}’ closes ‘{‘ before ‘[’ can be closed by ‘]’.

Example 3:

Input: String s = “(]”;
Expected Output: false
Explanation: The parentheses in this string are not balanced. Here, ‘)’ does not have a matching opening parenthesis ‘(‘, and similarly, ‘]’ does not have a matching opening bracket ‘[’.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64804bc840c761a52b2a872f

Question 113

Given an array of intervals representing ‘N’ appointments, find out if a person can attend all the appointments.

Example 1:

Appointments: [[1,4], [2,5], [7,9]]
Output: false
Explanation: Since [1,4] and [2,5] overlap, a person cannot attend both of these appointments.
Example 2:

Appointments: [[6,7], [2,4], [8,12]]
Output: true
Explanation: None of the appointments overlap, therefore a person can attend all of them.
Example 3:

Appointments: [[4,5], [2,3], [3,6]]
Output: false
Explanation: Since [4,5] and [3,6] overlap, a person cannot attend both of these appointments.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639363de4599b3e5714ab022

Question 114

Construct Binary Tree from Preorder and Inorder Traversal
Tech Interview Handbook
https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/

Question 115

Given an array, print the Next Greater Element (NGE) for every element.

The Next Greater Element for an element x is the first greater element on the right side of x in the array.

Elements for which no greater element exist, consider the next greater element as -1.

Examples
Example 1:

Input: [4, 5, 2, 25]
Output: [5, 25, 25, -1]
Example 1:

Input: [13, 7, 6, 12]
Output: [-1, 12, 12, -1]
Example 1:

Input: [1, 2, 3, 4, 5]
Output: [2, 3, 4, 5, -1]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/652377d9b28abf3c6db3b596

Question 116

Given a list of non-overlapping intervals sorted by their start time, insert a given interval at the correct position and merge all necessary intervals to produce a list that has only mutually exclusive intervals.

Example 1:

Input: Intervals=[[1,3], [5,7], [8,12]], New Interval=[4,6]
Output: [[1,3], [4,7], [8,12]]
Explanation: After insertion, since [4,6] overlaps with [5,7], we merged them into one [4,7].
Example 2:

Input: Intervals=[[1,3], [5,7], [8,12]], New Interval=[4,10]
Output: [[1,3], [4,12]]
Explanation: After insertion, since [4,10] overlaps with [5,7] & [8,12], we merged them into [4,12].
Example 3:

Input: Intervals=[[2,3],[5,7]], New Interval=[1,4]
Output: [[1,4], [5,7]]
Explanation: After insertion, since [1,4] overlaps with [2,3], we merged them into one [1,4].

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639245dffed07e597e96219f

Question 117

Sort Colors
Tech Interview Handbook
https://leetcode.com/problems/sort-colors/description/

Question 118

Given a string, identify the position of the first character that appears only once in the string. If no such character exists, return -1.

Examples

Example 1:

Input: “apple”
Expected Output: 0
Justification: The first character ‘a’ appears only once in the string and is the first character.
Example 2:

Input: “abcab”
Expected Output: 2
Justification: The first character that appears only once is ‘c’ and its position is 2.
Example 3:

Input: “abab”
Expected Output: -1
Justification: There is no character in the string that appears only once.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64b7b876aab5a6129791011e

Question 119

We are given an unsorted array containing n numbers taken from the range 1 to n. The array has some numbers appearing twice, find all these duplicate numbers using constant space.

Example 1:

Input: [3, 4, 4, 5, 5]
Output: [4, 5]
Example 2:

Input: [5, 4, 7, 2, 3, 5, 3]
Output: [3, 5]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6393b0a334689e585e94a29a

Question 120

Given an array of positive numbers and a positive number ‘k,’ find the maximum sum of any contiguous subarray of size ‘k’.

Example 1:

Input: [2, 1, 5, 1, 3, 2], k=3
Output: 9
Explanation: Subarray with maximum sum is [5, 1, 3].
Example 2:

Input: [2, 3, 4, 1, 5], k=2
Output: 7
Explanation: Subarray with maximum sum is [3, 4].

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/636b1d083b22faa3e89b2458

Question 121

Given a sorted linked list, remove all the duplicate elements to leave only distinct numbers. The linked list should remain sorted, and the modified list should be returned.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651014abfa9d768f431ff56c

Question 122

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:

Input: nums= [1, 2, 3, 4]
Output: false
Explanation: There are no duplicates in the given array.
Example 2:

Input: nums= [1, 2, 3, 1]
Output: true
Explanation: ‘1’ is repeating.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/63d8efe7f8694f3655d60712

Question 123

Binary Search
Tech Interview Handbook
https://leetcode.com/problems/binary-search/description/

Question 124

K Closest Points to Origin
Tech Interview Handbook
https://leetcode.com/problems/k-closest-points-to-origin/description/

Question 125

Given a sorted array, create a new array containing squares of all the numbers of the input array in the sorted order.

Example 1:

Input: [-2, -1, 0, 2, 3]
Output: [0, 1, 4, 4, 9]
Example 2:

Input: [-3, -1, 0, 1, 2]
Output: [0, 1, 1, 4, 9]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638e39bd1756319ef156bebc

Question 126

Given an array of integers, identify the highest value that appears only once in the array. If no such number exists, return -1.

Examples:

Example 1:

Input: [5, 7, 3, 7, 5, 8]
Expected Output: 8
Justification: The number 8 is the highest value that appears only once in the array.
Example 2:

Input: [1, 2, 3, 2, 1, 4, 4]
Expected Output: 3
Justification: The number 3 is the highest value that appears only once in the array.
Example 3:

Input: [9, 9, 8, 8, 7, 7]
Expected Output: -1
Justification: There is no number in the array that appears only once.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/64fd56f417ec3ee519760638

Question 127

Given an array nums sorted in increasing order, return the maximum between the count of positive integers and the count of negative integers.

Note: 0 is neither positive nor negative.

Examples
Example 1:

Input: nums = [-4, -3, -1, 0, 1, 3, 5, 7]
Expected Output: 4
Justification: The array contains three negative integers (-4, -3, -1) and four positive integers (1, 3, 5, 7). The maximum count between negatives and positives is 3.
Example 2:

Input: nums = [-8, -7, -5, -4, 0, 0, 0]
Expected Output: 4
Justification: Here, there are four negative integers (-8, -7, -5, -4) and no positives. Thus, the maximum count is 4.
Example 3:

Input: nums = [0, 2, 2, 3, 3, 3, 4]
Expected Output: 6
Justification: This input array includes zero negative integers and six positives (2, 2, 3, 3, 3, 4). Hence, the maximum count is 6.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/663ba7065ecab6da13d0a3f2

Question 128

Majority Element
Tech Interview Handbook
https://leetcode.com/problems/add-binary/description/

Question 129

Valid Palindrome
Tech Interview Handbook
https://leetcode.com/problems/valid-palindrome/description/

Question 130

Maximum Depth of Binary Tree
Tech Interview Handbook
https://leetcode.com/problems/maximum-depth-of-binary-tree/description/

Question 131

Word Break
Tech Interview Handbook
https://leetcode.com/problems/word-break/description/

Question 132

A pangram is a sentence where every letter of the English alphabet appears at least once.

Given a string sentence containing English letters (lower or upper-case), return true if sentence is a pangram, or false otherwise.

Note: The given sentence might contain other characters like digits or spaces, your solution should handle these too.

Example 1:

Input: sentence = “TheQuickBrownFoxJumpsOverTheLazyDog”
Output: true
Explanation: The sentence contains at least one occurrence of every letter of the English alphabet either in lower or upper case.
Example 2:

Input: sentence = “This is not a pangram”
Output: false
Explanation: The sentence doesn’t contain at least one occurrence of every letter of the English alphabet.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d923d6647c5c53032694bc

Question 133

Partition Equal Subset Sum
Tech Interview Handbook
https://leetcode.com/problems/partition-equal-subset-sum/description/

Question 134

Coin Change
Tech Interview Handbook
https://leetcode.com/problems/coin-change/description/

Question 135

Determine if a binary tree is height-balanced.

A binary tree is considered height-balanced if, for each node, the difference in height between its left and right subtrees is no more than one.

Examples:

Input:
3
/ \
9 20
/ \
15 7
Expected Output: true
Justification: Every node in the tree has a left and right subtree depth difference of either 0 or 1.
Input:
1
/ \
2 2
/ \ / \
3 3 3 3
/ \ / \
4 4 4 4
Expected Output: true
Justification: Each node in the tree has a left and right subtree depth difference of either 0 or 1.
Input:
1
/ \
2 5
/
3
/
4
Expected Output: false
Justification: The root node has a left subtree depth of 3 and right subtree depth of 1. The difference (3 - 1 = 2) exceeds 1, hence the tree is not balanced.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f27792576dc2031a7c48c6

Question 136

Given a string s, reverse only all the vowels in the string and return it.

The vowels are ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’, and they can appear in both lower and upper cases, more than once.

Example 1:

Input: s= “hello”
Output: “holle”
Example 2:

Input: s= “AEIOU”
Output: “UOIEA”
Example 3:

Input: s= “DesignGUrus”
Output: “DusUgnGires”

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d9b8744bb2155485a195e9

Question 137

Product of Array Except Self
Tech Interview Handbook
https://leetcode.com/problems/product-of-array-except-self/description/

Question 138

Merge Intervals
Tech Interview Handbook
https://leetcode.com/problems/merge-intervals/description/

Question 139

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

Example 1:

Input: sentence = “A man, a plan, a canal, Panama!”
Output: true
Explanation: “amanaplanacanalpanama” is a palindrome.
Example 2:

Input: sentence = “Was it a car or a cat I saw?”
Output: true
Explanation: Explanation: “wasitacaroracatisaw” is a palindrome.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d92beaa4af7161a01dff44

Question 140

Min Stack
Tech Interview Handbook
https://leetcode.com/problems/min-stack/description/

Question 141

Given a string, find the length of the longest substring in it with no more than K distinct characters.

You can assume that K is less than or equal to the length of the given string.

Example 1:

Input: String=”araaci”, K=2
Output: 4
Explanation: The longest substring with no more than ‘2’ distinct characters is “araa”.
Example 2:

Input: String=”araaci”, K=1
Output: 2
Explanation: The longest substring with no more than ‘1’ distinct characters is “aa”.
Example 3:

Input: String=”cbbebi”, K=3
Output: 5
Explanation: The longest substrings with no more than ‘3’ distinct characters are “cbbeb” & “bbebi”.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6384513a635674508787c7c3

Question 142

Given an array of unsorted numbers, find all unique triplets in it that add up to zero.

Example 1:

Input: [-3, 0, 1, 2, -1, 1, -2]
Output: [[-3, 1, 2], [-2, 0, 2], [-2, 1, 1], [-1, 0, 1]]
Explanation: There are four unique triplets whose sum is equal to zero. smallest sum.’
Example 2:

Input: [-5, 2, -1, -2, 3]
Output: [[-5, 2, 3], [-2, -1, 3]]
Explanation: There are two unique triplets whose sum is equal to zero.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638f6ff2ae53511bdc36490d

Question 143

Minimum Height Trees
Tech Interview Handbook
https://leetcode.com/problems/minimum-height-trees/description/

Question 144

Given a non-negative integer x, return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well.

You must not use any built-in exponent function or operator.

For example, do not use pow(x, 0.5) in c++ or x ** 0.5 in python.

Example 1:

Input: x = 8
Output: 2
Explanation: The square root of 8 is 2.8284, and since we need to return the floor of the square root (integer), hence we returned 2.
Example 2:

Input: x = 4
Output: 2
Explanation: The square root of 4 is 2.
Example 3:

Input: x = 2
Output: 1
Explanation: The square root of 2 is 1.414, and since we need to return the floor of the square root (integer), hence we returned 1.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d8fcaae8462840e6bde243

Question 145

Given a binary tree, populate an array to represent its level-by-level traversal. You should populate the values of all nodes of each level from left to right in separate sub-arrays.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6394fcd622692a384ae7dbdd

Question 146

Give a string s, convert it into a valid string. A string is considered valid if it does not have any two adjacent duplicate characters.

To make a string valid, we will perform a duplicate removal process. A duplicate removal consists of choosing two adjacent and equal letters and removing them. We repeatedly make duplicate removals on s until we no longer can.

Return the final string after all such duplicate removals have been made.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64903910024dfda098f3aa6f

Question 147

Ransom Note
Tech Interview Handbook
https://leetcode.com/problems/ransom-note/description/

Question 148

Merge Two Sorted Lists
Tech Interview Handbook
https://leetcode.com/problems/merge-two-sorted-lists/description/

Question 149

Given a binary tree and a node, find the level order successor of the given node in the tree. The level order successor is the node that appears right after the given node in the level order traversal.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/639894f2e4cab4072de783e2

Question 150

Spiral Matrix
Tech Interview Handbook
https://leetcode.com/problems/spiral-matrix/description/

Question 151

Given a string, identify the length of its longest segment that contains distinct characters. In other words, find the maximum length of a substring that has no repeating characters.

Examples:

Example 1:

Input: “abcdaef”
Expected Output: 6
Justification: The longest segment with distinct characters is “bcdaef”, which has a length of 6.
Example 2:

Input: “aaaaa”
Expected Output: 1
Justification: The entire string consists of the same character. Thus, the longest segment with unique characters is just “a”, with a length of 1.
Example 3:

Input: “abrkaabcdefghijjxxx”
Expected Output: 10
Justification: The longest segment with distinct characters is “abcdefghij”, which has a length of 10.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64fd71c1d3fee58156fd1fb5

Question 152

You are given a 2D matrix containing different characters, you need to find if there exists any cycle consisting of the same character in the matrix.

A cycle is a path in the matrix that starts and ends at the same cell and has four or more cells. From a given cell, you can move to one of the cells adjacent to it - in one of the four directions (up, down, left, or right), if it has the same character value of the current cell.

Write a function to find if the matrix has a cycle.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638c9a7688f1e1c16f41bb3c

Question 153

Insert Interval
Tech Interview Handbook
https://leetcode.com/problems/insert-interval/description/

Question 154

3Sum
Tech Interview Handbook
https://leetcode.com/problems/3sum/description/

Question 155

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:

Input: nums= [1, 2, 3, 4]
Output: false
Explanation: There are no duplicates in the given array.
Example 2:

Input: nums= [1, 2, 3, 1]
Output: true
Explanation: ‘1’ is repeating.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63d8efe7f8694f3655d60712

Question 156

Given an array of numbers sorted in ascending order and a target sum, find a pair in the array whose sum is equal to the given target.

Write a function to return the indices of the two numbers (i.e. the pair) such that they add up to the given target. If no such pair exists return [-1, -1].

Example 1:

Input: [1, 2, 3, 4, 6], target=6
Output: [1, 3]
Explanation: The numbers at index 1 and 3 add up to 6: 2+4=6
Example 2:

Input: [2, 5, 9, 11], target=11
Output: [0, 2]
Explanation: The numbers at index 0 and 2 add up to 11: 2+9=11

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638ca0aa5b41522e8a2e3395

Question 157

Letter Combinations of a Phone Number
Tech Interview Handbook
https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/

Question 158

Given a binary tree, return an array containing nodes in its right view. The right view of a binary tree is the set of nodes visible when the tree is seen from the right side.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63989ddfa1cb64009de121d1

Question 159

Given a directed acyclic graph with n nodes labeled from 0 to n-1, determine the smallest number of initial nodes such that you can access all the nodes by traversing edges. Return these nodes.

Examples
Input:

n = 6
edges = [[0,1],[0,2],[2,5],[3,4],[4,2]]
Expected Output: [0,3]

Justification: Starting from nodes 0 and 3, you can reach all other nodes in the graph. Starting from node 0, you can reach nodes 1, 2, and 5. Starting from node 3, you can reach nodes 4 and 2 (and by extension 5).

Input:

n = 3
edges = [[0,1],[2,1]]
Expected Output: [0,2]

Justification: Nodes 0 and 2 are the only nodes that don’t have incoming edges. Hence, you need to start from these nodes to reach node 1.

Input:

n = 5
edges = [[0,1],[2,1],[3,4]]
Expected Output: [0,2,3]

Justification: Node 1 can be reached from both nodes 0 and 2, but to cover all nodes, you also need to start from node 3.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/651a85ec58fd4e18cd6e4fe3

Question 160

Given a square matrix (2D array), calculate the sum of its two diagonals.

The two diagonals in consideration are the primary diagonal that spans from the top-left to the bottom-right and the secondary diagonal that spans from top-right to bottom-left. If a number is part of both diagonals (which occurs only for odd-sized matrices), it should be counted only once in the sum.

Examples
Example 1:
Input:
[[1,2,3],
[4,5,6],
[7,8,9]]
Expected Output: 25
Justification: Summing up the two diagonals (1+5+9+3+7), we get 25. Please note that the element at [1][1] = 5 is counted only once.
Example 2:
Input:
[[1,0],
[0,1]]
Expected Output: 2
Justification: The sum of the two diagonals is 1+1 = 2.
Example 3:
Input:
[[5]]
Expected Output: 5
Justification: Since there’s only one element, it is the sum itself.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/651bbcf208261ac5b3b37904

Question 161

Given a string of English lowercase and uppercase letters, make the string “good” by removing two adjacent characters that are the same but in different cases.

Continue to do this until there are no more adjacent characters of the same letter but in different cases. An empty string is also considered “good”.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64904f9272f95964a978090e

Question 162

You are given a 2D matrix containing only 1s (land) and 0s (water).

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

A closed island is an island that is totally surrounded by 0s (i.e., water). This means all horizontally and vertically connected cells of a closed island are water. This also means that, by definition, a closed island can’t touch an edge (as then the edge cells are not connected to any water cell).

Write a function to find the number of closed islands in the given matrix.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/638c7f5bb2790984e1934f98

Question 163

Any image can be represented by a 2D integer array (i.e., a matrix) where each cell represents the pixel value of the image.

Flood fill algorithm takes a starting cell (i.e., a pixel) and a color. The given color is applied to all horizontally and vertically connected cells with the same color as that of the starting cell. Recursively, the algorithm fills cells with the new color until it encounters a cell with a different color than the starting cell.

Given a matrix, a starting cell, and a color, flood fill the matrix.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6388e8887b259e5c9e8c0274

Question 164

Maximum Subarray
Tech Interview Handbook
https://leetcode.com/problems/maximum-subarray/description/

Question 165

Any number will be called a happy number if, after repeatedly replacing it with a number equal to the sum of the square of all of its digits, leads us to the number 1. All other (not-happy) numbers will never reach 1. Instead, they will be stuck in a cycle of numbers that does not include 1.

Given a positive number n, return true if it is a happy number otherwise return false.

Example 1:

Input: 23
Output: true (23 is a happy number)
Explanations: Here are the steps to find out that 23 is a happy number:

= 4 + 9 = 13
= 1 + 9 = 10
= 1 + 0 = 1

Example 2:

Input: 12
Output: false (12 is not a happy number)
Explanations: Here are the steps to find out that 12 is not a happy number:

= 1 + 4 = 5
= 25
= 4 + 25 = 29
= 4 + 81 = 85
= 64 + 25 = 89
= 64 + 81 = 145
= 1 + 16 + 25 = 42
= 16 + 4 = 20
= 4 + 0 = 4
= 16
= 1 + 36 = 37
= 9 + 49 = 58
= 25 + 64 = 89

Please note the cycle from 89 -> 89.

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63911273cf5aba4f2f70b5fe

Question 166

Two Sum
Tech Interview Handbook
https://leetcode.com/problems/two-sum/description/

Question 167

Given an unsorted array containing numbers, find the smallest missing positive number in it.

Note: Positive numbers start from ‘1’.

Example 1:

Input: [-3, 1, 5, 4, 2]
Output: 3
Explanation: The smallest missing positive number is ‘3’
Example 2:

Input: [3, -2, 0, 1, 2]
Output: 4
Example 3:

Input: [3, 2, 5, 1]
Output: 4
Example 4:

Input: [33, 37, 5]
Output: 1

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/63948c59c549a12fb2181118

Question 168

Given a 2D array (i.e., a matrix) containing only 1s (land) and 0s (water), count the number of islands in it.

An island is a connected set of 1s (land) and is surrounded by either an edge or 0s (water). Each cell is considered connected to other cells horizontally or vertically (not diagonally).

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6388cbb0765bb2154037ce84

Question 169

Given a Binary Search Tree (BST), you are required to find the smallest difference between the values of any two different nodes.

In a BST, the nodes are arranged in a manner where the value of nodes on the left is less than or equal to the root, and the value of nodes on the right is greater than the root.

Example

Example 1:

Input:
4
/ \
2 6
/ \
1 3
Expected Output: 1
Justification: The pairs (1,2), (2,3), or (3,4) have the smallest difference of 1.
Example 2:

Input:
10
/ \
5 15
/ \ \
2 7 18
Expected Output: 2
Justification: The pair (5,7) has the smallest difference of 2.
Example 3:

Input:
40
\
70
/ \
50 90
Expected Output: 10
Justification: The pair (40,50) has the smallest difference of 10.

https://www.designgurus.io/course-play/grokking-data-structures-for-coding-interviews/doc/64f2861edc5301795f81328f

Question 170

You are visiting a farm to collect fruits. The farm has a single row of fruit trees. You will be given two baskets, and your goal is to pick as many fruits as possible to be placed in the given baskets.

You will be given an array of characters where each character represents a fruit tree. The farm has following restrictions:

Each basket can have only one type of fruit. There is no limit to how many fruit a basket can hold.
You can start with any tree, but you can’t skip a tree once you have started.
You will pick exactly one fruit from every tree until you cannot, i.e., you will stop when you have to pick from a third fruit type.
Write a function to return the maximum number of fruits in both baskets.

Example 1:

Input: arr=[‘A’, ‘B’, ‘C’, ‘A’, ‘C’]
Output: 3
Explanation: We can put 2 ‘C’ in one basket and one ‘A’ in the other from the subarray [‘C’, ‘A’, ‘C’]
Example 2:

Input: arr = [‘A’, ‘B’, ‘C’, ‘B’, ‘B’, ‘C’]
Output: 5
Explanation: We can put 3 ‘B’ in one basket and two ‘C’ in the other basket. This can be done if we start with the second letter: [‘B’, ‘C’, ‘B’, ‘B’, ‘C’]

https://www.designgurus.io/course-play/grokking-the-coding-interview/doc/6385d2dae25dea6343fd8b19