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]]

模拟一下，先看四个角，每次交换两个，交换三次就可以了。对于左上角向下走一个单位找到a，左下角向右移动一个单位b，右下角向上移动c，右上角向左移动d。交换(a,b)(b,c),(c,d)....

具体见代码:

class Solution {public:    void rotate(vector
    
     
      >& matrix) {        int n = matrix.size();        if (n == 0) return ;        int x = n/2;        int y = n;        for (int p = 0; p < x; ++p) {            for (int i = 0; i <= y - 2; ++i) {                swap(matrix[p+i][p], matrix[n-p-1][p+i]);                swap(matrix[n-p-1][p+i], matrix[n-p-1-i][n-p-1]);                swap(matrix[n-p-1-i][n-p-1], matrix[p][n-p-1-i]);            }            y -= 2;        }    }};