Merge Sorted Array LeetCode Solution

Difficulty Level Easy
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Problem Statement

Merge Sorted Array LeetCode Solution – 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

Test Case 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.

Approach:

Solution 01

  • We took j=0 to iterate nums2 from the beginning.
  • As we know nums1 has a size of m+n & only the first m elements should be in the final array.
  • So we replace all the elements from the m index with all the elements of nums2.
  • Finally, we’ll sort the array nums1 to get the final sorted array.
  • Time complexity: O(nlogn) //as sorting takes nlogn time.

Solution 02

  • Same logic as Solution 01, But here we used resize().
  • Resize() will simply keep the elements till m index in muns1 array.
  • Then we’ll insert all the elements of the nums2 array by using insert().
  • Lastly, we’ll sort the array nums1 to get the final sorted array.
  • Time complexity: O(nlogn) //as sorting takes nlogn time.

Solution 03

  • As both solutions 01 & 02 take O(nlogn), now we try to solve it with O(n+m).
  • We will use the reverse sorting method.
  • We took 3 variables: i (last valid element of nums1 that will present in the final array), j (last element of nums2) & k ( last index of nums1)
  • First, while loop will compare nums1 & nums2, and the greater element will be in nums1[k].
  • After the loop end if there are still any elements left in an array they will be added by the next 2 while loop.
  • Time complexity: O(m+n).

Merge Sorted Array LeetCode SolutionPin

Code for Merge Sorted Array

Python Program

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        i, j, cur = m - 1, n - 1, m + n - 1
        
        while j > -1:
            if i > -1 and nums1[i] >= nums2[j]:
                nums1[cur] = nums1[i]
                i -= 1
            else:
                nums1[cur] = nums2[j]
                j -= 1
            
            cur -= 1

Java Program

class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int last1 = m-1;
        int last2 = n-1;
        
        int index = nums1.length-1;
        
        while (last1 >=0 && last2>=0) {
            int l = nums1[last1];
            int r = nums2[last2];
            
            if (l < r) {
                nums1[index--] = r;
                last2--;
            } else {
                nums1[index--] = l;
                last1--;
            }
        }
        
        while (last2 >=0) {
            int r = nums2[last2];
            
            nums1[index--] = r;
            last2--;
        }
    }
}

Complexity Analysis for Merge Sorted Array LeetCode Solution

Time Complexity: O(m+n) where m and n are the number of non-zero elements in nums1 and nums2 respectively since we are iterating over both arrays in order to merge them

Space Complexity: O(1) since we are doing the merging in place.

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