## Description

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Note:

• The number of elements initialized in nums1 and nums2 are m and n respectively.
• You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2.

Example:

Input:
nums1 = [1,2,3,0,0,0], m = 3
nums2 = [2,5,6],       n = 3

Output: [1,2,2,3,5,6]


## Solutions

从后往前进行判断，注意在比较大小满足退出条件时，第二个数组可能还没有遍历完，需要补充进去。

# Time: O(n+m)
# Space: O(1)
class Solution:
def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
"""
Do not return anything, modify nums1 in-place instead.
"""
a, b = m - 1, n - 1
i = m + n - 1
while i >= 0 and a >= 0 and b >= 0:
if nums1[a] > nums2[b]:
nums1[i] = nums1[a]
a -= 1
else:
nums1[i] = nums2[b]
b -= 1
i -= 1
if b >= 0:
nums1[:b+1] = nums2[:b+1]

# 59/59 cases passed (36 ms)
# Your runtime beats 56.75 % of python3 submissions
# Your memory usage beats 100 % of python3 submissions (12.9 MB)