https://leetcode.com/problems/merge-sorted-array/
题目：
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 nums1and nums2 are m and n respectively.
思路：
利用好nums1后n个空闲的空间是关键。
AC代码：
1 class Solution {
2 public:
3 void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
4 int i1 = m - 1, i2 = n - 1, k = m + n - 1;
5 while (i1>= 0 && i2>=0){
6 if (nums1[i1] < nums2[i2])
7 {
8 nums1[k--] = nums2[i2--];
9 }
10 else{
11 nums1[k--] = nums1[i1--];
12 }
13 }
14 while (i2 >= 0){
15 nums1[k--] = nums2[i2--];
16 }
17
18 return;
19 }
20 };