leetcode : merge two sorted array

key: tranverse from the last index;  

three point: m-1, n-1; m+n-1;

void merge(int A[], int m, int B[], int n) {
        int i = m-1;
        int j = n-1;
        int start = m+n-1;
        while(i >=0 && j >= 0){
            if(A[i] < B[j]){
                A[start--] = B[j--];
            }else{
                A[start--] = A[i--];
            }
        }
        if(i < 0){
            while(j >= 0){
                A[start--] = B[j--];
            }
        }
}