LeetCode--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]
]

思路：找规律。通过观察法找规律发现，先将矩阵元素按行颠倒翻转，然后再将关于对角线对称的元素互换，转置即可。

class Solution {public:    void rotate(vector<vector<int>>& matrix) {        reverse(matrix.begin(),matrix.end());        for(int i=0;i<matrix.size();i++){            for(int j=i+1;j<matrix[0].size();j++){                swap(matrix[i][j],matrix[j][i]);            }        }    }};