Arrays and Strings

Question 1

How would you swap values in a list or an array? Used for reversing an array.

Answer 1

Two approaches to reverse:
1. By creating a new array of same size then starting from the end populate this new array. Drawback is we get space complexity of O(N) along with time O(N)
2. In-place technique
Two pointer technique in which you use two pointers either you use it to exchange/swap values. You remove the space complexity and time is pretty similar O(N/2) ~ O(N)

Question 2

How to reverse words in a string?

Answer 2

Can reverse the entire string and then reverse each word using two pointer technique

Question 3

How to find max or min number of items in an array that appear consecutively?

Example:
Input: [1, 1, 2, 2, 2]
Output : 3 (2 occurs thrice)

Answer 3

Determine what is the starting point of a window (consecutive items) and then determine how to end that window

Question 4

How to find the integer that occurs once in an array of integers in which there are exactly two occurrences of every value except for one?

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

Answer 4

Hashmap can be using to keep track of counts

In ONLY this scenario where there are exactly TWO occurrences we can do bit manipulation (XOR)

class Solution {
  public int singleNumber(int[] nums) {
    int a = 0;
    for (int i : nums) {
      a ^= i;
    }
    return a;
  }
}

Question 5

How to find distinct values in a list

Answer 5

Use one slow pointer and other faster. move the faster pointer till you find a non distinct value and then swap with the value that repeats

class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums.length == 0 || nums.length == 1)
          {
             return nums.length;
          }

        int i =0;
        for (int j = 1; j< n; j ++) {
           if (nums[i] != nums[j]) {
               i++;
               nums[i] = nums[j];
           } 
       }
        return j+1;
    }
}

Question 6

Parentheses problem

Answer 6

Stacks and recursion

Question 7

What does ArrayList set method do?

Answer 7

public E set(int index, Element E)

If there is a need to update the list element based on the index then set method of ArrayList class can be used. The method set(int index, Element E) updates the element of specified index with the given element E.

Question 8

How to copy a specific range of integers from an array?

Answer 8

Java:
Arrays.copyOfRange(arr, startIdx, endIdx)

C#:
Array.Copy(sourceArr, , destinationArr, , length)

Question 9

If you have to do any sorting operation on array using O(n), what approach you should be targeting at

Answer 9

Try to see if you can use two pointer approach for that problem

Question 10

Using base64 encode, a 6 letter long key could give you how many combinations

Answer 10

[64^6] possible strings

Question 11

if we have a string or arr of chars arr that are int values, like “0000”, “1100”, ‘0’ then how to convert char into an int

Answer 11

(arr[i] - ‘0’)

so if arr[i] was ‘1’, the above will give
(int)’1’ - (int)’0’ = 49-48 = 1

Question 12

How to identify diagonals on a chessboard (or 2D matrix)

Answer 12

For each square on a given diagonal the (row - column) will be the same

Question 13

How to then identify the anti-diagonal (diagonal orthogonal) on a chessboard (or 2D matrix):

Answer 13

For each square on an anti-diagonal the (row + column) will be the same

Question 14

Jagged array (array of array) declaration:

Answer 14

int[][] x = new int[2][];

note that the index is empty in the RHS

Question 15

Uniform 2D Array declaration:

Answer 15

int[,] x = new int[2,2];