Merge Sorted Array Problem & 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.

See the merge sorted array problem on LeetCode.

C++ Solution

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")

static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

class Solution {
  void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
    int k = m + n - 1;
    int i = m - 1;
    int j = n - 1;

    while (i >= 0 && j >= 0) {
      if (nums1[i] > nums2[j]) {
        nums1[k--] = nums1[i--];
      } else {
        nums1[k--] = nums2[j--];

    while (j >= 0) {
      nums1[k--] = nums2[j--];

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