https://leetcode.com/problems/merge-sorted-array/description/

class Solution {public:    void merge(vector
     
      & nums1, int m, vector
      
       & nums2, int n) {        int i = m - 1, j = n - 1, k = m + 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--];        }    }};