Leetcode - Array - Merge Sorted Array

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.

class Solution {
public:
void merge(int A[], int m, int B[], int n) {
if(A==NULL||m<0||B==NULL||n<0)
return;
reverse(A,A+m+n);
reverse(A+n,A+m+n);
int indexA=n,indexB=0,index=0;
while(indexA<m+n&&indexB<n)
{
if(A[indexA]<=B[indexB])
A[index++]=A[indexA++];
else
A[index++]=B[indexB++];
}
while(indexB<n)
A[index++]=B[indexB++];
}
};