//time:o(n)
//space:o(1)

class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int i = m-1;
        int j = n-1;
        int k = m+n-1;
        while(i>=0 && j>=0){
            nums1[k--] = nums1[i]>=nums2[j]?
                nums1[i--]:nums2[j--];
        }
         while(j >= 0 )  {
            nums1[k--] = nums2[j--];
        }
    }
}