LeetCode—Merge Sorted Array两个有序数组排序

Given two sorted integer arrays A and B, merge B into A as one sorted array.

Note:

You may assume that A has enough space (size that is greater or equal to m + n) to hold additional elements from B. The number of elements initialized in A and B are m andn respectively.
这里比较好的一个条件就是数组A是已经给定了存储空间的数组，这样的一个merge函数在归并算法中经常会用到

第一种应该是最愚蠢的做法，重新开辟了一个m+n的内存空间

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        int *C = new int[m+n];
        int i = 0;
        int j = 0;
        int k = 0;
        while(i < m && j < n)
        {
            if(A[i] <= B[j])
            {
                C[k++] = A[i++];
            }
            if(A[i] > B[j])
            {
                C[k++] = B[j++];
            }
        }
        while(i < m)
        {
            C[k++] = A[i++];
        }
        while(j < n)
        {
            C[k++] = B[j++];
        }
        for(i = 0; i < k;i++)
        {
            A[i] = C[i];
        }
        delete []C;
    }
};

但是题目中已经提到A数组是有序的，而且长度很大，应该合理利用这个信息：

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        int i = m-1;
        int j = n-1;
        int k= m+n-1;
        while(i >= 0 && j >= 0)
        {
            if(A[i] >= B[j])
            {
                A[k--] = A[i--];
            }
            if(A[i] < B[j])
            {
                A[k--] = B[j--];
            }
        }
        while(j >= 0)
        {
            A[k--] = B[j--];
        }
    }
};