# Leetcode Python超琐碎笔记: 832. Flipping an Image

### 问题描述

Given a binary matrix `A`, we want to flip the image horizontally, then invert it, and return the resulting image.

To flip an image horizontally means that each row of the image is reversed. For example, flipping `[1, 1, 0]` horizontally results in `[0, 1, 1]`.

To invert an image means that each `0` is replaced by `1`, and each `1` is replaced by `0`. For example, inverting `[0, 1, 1]` results in `[1, 0, 0]`.

Example 1:

Input: [[1,1,0],[1,0,1],[0,0,0]]
Output: [[1,0,0],[0,1,0],[1,1,1]]
Explanation: First reverse each row: [[0,1,1],[1,0,1],[0,0,0]].
Then, invert the image: [[1,0,0],[0,1,0],[1,1,1]]

Example 2:

Input: [[1,1,0,0],[1,0,0,1],[0,1,1,1],[1,0,1,0]]
Output: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]
Explanation: First reverse each row: [[0,0,1,1],[1,0,0,1],[1,1,1,0],[0,1,0,1]].
Then invert the image: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]

Notes:
`1 <= A.length = A[0].length <= 20`
`0 <= A[i][j] <= 1`

### 我的实现及调优过程

##### 方法1：76 ms
``````class Solution:
def flipAndInvertImage(self, A):
"""
:type A: List[List[int]]
:rtype: List[List[int]]
"""
A = [row[::-1] for row in A]
A = [list(map(lambda x: 1-x, row)) for row in A]
return A
``````

• 时间复杂度：NA
• 空间复杂度：NA
##### 方法2：48 ms
``````class Solution:
def flipAndInvertImage(self, A):
"""
:type A: List[List[int]]
:rtype: List[List[int]]
"""
A = [row[::-1] for row in A]
A = [list(map(lambda x: x^1, row)) for row in A]
return A
``````

• 时间复杂度：NA
• 空间复杂度：NA
##### 方法3：72 ms
``````class Solution:
def flipAndInvertImage(self, A):
"""
:type A: List[List[int]]
:rtype: List[List[int]]
"""
for row in A:
i = 0
j = len(row) - 1
while (i <= j):
row[i], row[j] = row[j]^1, row[i]^1
i += 1
j -= 1
return A
``````

• 时间复杂度：O(m*n) （m为矩阵行数，n为列数）
• 空间复杂度：O(m)
##### 方法4：48 ms
``````class Solution:
def flipAndInvertImage(self, A):
"""
:type A: List[List[int]]
:rtype: List[List[int]]
"""
for row in A:
for i in range((len(row)+1)//2): # for both even/odd row length
row[i], row[~i] = row[~i]^1, row[i]^1
return A
``````

• 列数为奇数，以3为例：`(3+1)//2 = 2``range`后得到[0,1]
• 列数为偶数，以4为例：`(4+1)//2 = 2``range`后得到[0,1]

• 时间复杂度：O(m*n) （m为矩阵行数，n为列数）
• 空间复杂度：O(m)