https://leetcode.com/problems/merge-sorted-array/
因为这里要求in place 修改nums1.所以不要新申请一个list。小trick就是two pointers 从list末尾开始scan。最后要注意n > m的时候，还要把剩余的nums2加到nums1中
http://chaoren.is-programmer.com/posts/42844.html
class Solution(object):
def merge(self, nums1, m, nums2, 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,j,k = m - 1, n - 1, m + n - 1
while i >= 0 and j >= 0:
if nums1[i] > nums2[j]:
nums1[k] = nums1[i]
i -= 1
else:
nums1[k] = nums2[j]
j -= 1
k -= 1
while j >= 0:
nums1[k] = nums2[j]
j -= 1
k -= 1