LeetCode Merge Sorted Array

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Note:
You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectively.

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        /*
        //从前向后比较开销很大
        for(int i = m-1; i>=0; i--)
            nums1[i+n] = nums1[i];
        int ptr1 = n, ptr2 = 0, index = 0;
        while(ptr1 < m + n && ptr2 < n){
            if(nums1[ptr1] < nums2[ptr2])
                nums1[index++] = nums1[ptr1++];
            else nums1[index++] = nums2[ptr2++];
        }
        while(ptr2 < n)
            nums1[index++] = nums2[ptr2++];
        */
        int ptr1 = m - 1, ptr2 = n - 1, index = m + n - 1;
        while(ptr1 >= 0 && ptr2 >= 0){
            if(nums1[ptr1] > nums2[ptr2])
                nums1[index--] = nums1[ptr1--];
            else nums1[index--] = nums2[ptr2--];
        }
        while(ptr2 >= 0)
            nums1[index--] = nums2[ptr2--];
    }
};

注：从后向前比较开销较小，从前向后比较，需要整体向后移动nums1数组，导致比较大的开销。