# 48. Rotate Image 旋转图像

@TOC

## # 题目描述

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note: You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

``````Given input matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
``````

Example 2:

``````Given input matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],

rotate the input matrix in-place such that it becomes:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
``````

## # 解题方法

``````class Solution(object):
def rotate(self, matrix):
"""
:type matrix: List[List[int]]
:rtype: void Do not return anything, modify matrix in-place instead.
"""
if matrix:
rows = len(matrix)
cols = len(matrix[0])
for i in xrange(rows / 2):
for j in xrange(cols):
matrix[i][j], matrix[rows - i - 1][j] = matrix[rows - i - 1][j], matrix[i][j]
for i in xrange(rows):
for j in xrange(i):
matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
``````

``````class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
if (!matrix.size()) return;
const int N = matrix.size();
for (int i = 0; i < N; i ++) {
for (int j = 0; j < N / 2; j ++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[i][N - j - 1];
matrix[i][N - j - 1] = tmp;
}
}
for (int i = 0; i < N; i ++) {
for (int j = 0; j < N - i; j ++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[N - j - 1][N - i - 1];
matrix[N - j - 1][N - i - 1] = tmp;
}
}
}
};
``````

## # 日期

2018 年 3 月 5 日 2018 年 12 月 30 日 —— 周赛差强人意