Merge Sorted Array

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

Example
A = [1, 2, 3, empty, empty], B = [4, 5]

After merge, A will be filled as [1, 2, 3, 4, 5]

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 and n respectively.

class Solution {
    /**
     * @param A: sorted integer array A which has m elements, 
     *           but size of A is m+n
     * @param B: sorted integer array B which has n elements
     * @return: void
     */
     public void mergeSortedArray(int[] A, int m, int[] B, int n) {
        if (A == null || B == null) return;

        int index = m + n - 1;
        while (m > 0 && n > 0) {
            if (A[m - 1] > B[n - 1]) {
                A[index] = A[m - 1];
                m--;
            } else {
                A[index] = B[n - 1];
                n--;
            }
            index--;
        }

        // B has elements left
        while (n > 0) {
            A[index] = B[n - 1];
            n--;
            index--;
        }
    }
}