88. Merge Sorted Array（从后向前复制）

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.

nums1已经是m+n长度了，不用新申请空间。

从后向前复制。

 class Solution:
     def merge(self, l1, m, l2, n):
         """
         :type nums1: List[int]
         :type m: int
         :type nums2: List[int]
         :type n: int
         :rtype: void Do not return anything, modify nums1 in-place instead.
         """
         i = m - 1
         j = n - 1

         end = m+n-1
         while(i >= 0 and j >= 0):
             if(l1[i] > l2[j]):
                 l1[end] = l1[i]
                 i-=1
             else:
                 l1[end] = l2[j]
                 j -= 1
             end -=1

         while (j>=0):
             l1[end] = l2[j]
             j -= 1
             end-=1