【LeetCode & 剑指offer 刷题笔记】目录（持续更新中...）
Rotate Image
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]
]
//问题：旋转图像（要求：原地顺时针旋转90°）
/*
* 顺时针旋转方法：先上下翻转，再沿对角线翻转
* clockwise rotate
* first reverse up to down, then swap the symmetry
* 1 2 3 7 8 9 7 4 1
* 4 5 6 => 4 5 6 => 8 5 2
* 7 8 9 1 2 3 9 6 3
*/
#include <algorithm>
class Solution
{
public:
void rotate(vector<vector<int>>& matrix)
{
reverse(matrix.begin(), matrix.end()); //stl中函数,对每列reverse,直接reverse matrix即可
for(int i = 0; i< matrix.size(); i++)
{
for(int j = i+1; j < matrix[i].size(); j++) //注意这里j从i+1开始，因为只需对一半元素执行操作，i=0,j=1~n-1;i=1,j=2~n-1...
{
swap(matrix[i][j], matrix[j][i]);
}
}
}
};
/*
* * 逆时针旋转方法：先左右翻转，再沿对角线翻转
* anticlockwise rotate
* first reverse left to right, then swap the symmetry
* 1 2 3 3 2 1 3 6 9
* 4 5 6 => 6 5 4 => 2 5 8
* 7 8 9 9 8 7 1 4 7
*/
/*
void anti_rotate(vector<vector<int> > &matrix) {
for (auto vi : matrix) reverse(vi.begin(), vi.end()); //对每行reverse,故要遍历matrix，reverse内部容器
for (int i = 0; i < matrix.size(); ++i) {
for (int j = i + 1; j < matrix[i].size(); ++j)
swap(matrix[i][j], matrix[j][i]);
}
}
*/