输入：nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
输出：[1,2,2,3,5,6]

输入：nums1 = [1], m = 1, nums2 = [], n = 0
输出：[1]

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