88. Merge Sorted Array

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.

Follow up: Can you come up with an algorithm that runs in O(m + n) time?

• Time : O(n + m)
• Space : O(1)

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        if(!n) return;
        int p1 = m -1, p2 = n - 1;
        for(int i = m + n - 1; i >= 0 and p1 >= 0 and p2 >= 0; i--) {
            if(nums1[p1] >= nums2[p2]) {
                nums1[i] = nums1[p1--];
            } else {
                nums1[i] = nums2[p2--];
            }
        }
        for(int i = 0; i <= p2; i++) {
            nums1[i] = nums2[i];
        }
    }
};