Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.
Note:
You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectively.

Solution：Two Pointers

思路：其实和new一个result数组 然后对两个排好序的序列merge 的思路一样。只不过这里利用的是num1后面的多余空间。
Time Complexity: O(N) Space Complexity: O(1)

Solution Code：

class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        if(n == 0) return;
        
        int index1 = m - 1, index2 = n - 1;
        
        int k = m + n - 1;
        while(index1 >= 0 && index2 >= 0) {
            if(nums1[index1] > nums2[index2]) {
                nums1[k--] = nums1[index1--];
            }
            else {
                nums1[k--] = nums2[index2--];
            }
        }
        while(index2 >= 0) nums1[k--] = nums2[index2--];
        // while(index1 >= 0) nums1[k--] = nums1[index1--];
    }
}