原题是：
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.
Screen Shot 2017-11-22 at 10.08.40 PM.png
思路是：
这个题，如果要不断比较两个数组的元素，然后插入，需要挪动大量元素的位置，且是多次，时间复杂度太大。
那么我们可以借助第一个数组后面“空”出来的空间，从后向前依次“排队”。
代码是：
class Solution:
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 = m-1,n-1
cnt = 1
while i > -1 and j > -1 :
if nums1[i] > nums2[j]:
nums1[m + n - cnt] = nums1[i]
i -= 1
else:
nums1[m + n - cnt] = nums2[j]
j -= 1
cnt += 1
if i == -1:
for p in range(0,j+1):
nums1[p] = nums2[p]
