Arrays

Question 1

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively.

Merge nums1 and nums2 into a single array sorted in non-decreasing order.

The final sorted array should not be returned by the function, but instead be stored inside the array nums1. To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, and the last n elements are set to 0 and should be ignored. nums2 has a length of n.

Example 1:

Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Explanation: The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [1,2,2,3,5,6] with the underlined elements coming from nums1.

Answer 1

class Solution {
public void merge(int[] nums1, int m, int[] nums2, int n) {

  int e1=m-1;
  int e2=n-1;
  int curr=nums1.length-1;
  
  while(curr>=0)
  {
    if(e1 <0)
    {
      nums1[curr]=nums2[e2];
      e2--;
    }
    else if(e2 < 0)
    {
      nums1[curr]=nums1[e1];
      e1--;
    }
    else {
      if(nums1[e1]>nums2[e2])
      {
        nums1[curr]=nums1[e1];
        e1--;
      }
      else
      {
        nums1[curr]=nums2[e2];
        e2--;
      }
    }
    curr--;
    
  }
} }

Question 2

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.

A subarray is a contiguous non-empty sequence of elements within an array.

Example 1:

Input: nums = [1,1,1], k = 2
Output: 2
Example 2:

Input: nums = [1,2,3], k = 3
Output: 2

Answer 2

class Solution {
public int subarraySum(int[] nums, int k) {

    Map<Integer,Integer> hm = new HashMap<>();

    int count =0;
    int sum =0;
    hm.put(0,1);
    for(int i =0; i<nums.length;i++){
        sum = sum+nums[i];

        if(hm.containsKey(sum-k)) {
            count= count+ hm.get(sum -k);
        }

        hm.put(sum, hm.getOrDefault(sum, 0)+1);

    }

    return count;

    
} }