LeetCode Rotate Image

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

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

题意：矩阵旋转。

思路：每次旋转的时候都一次性旋转4个数。

class Solution {public:    void rotate(vector<vector<int> > &matrix) {        int n = matrix.size() - 1;        for (int i = 0; i < n; i++) {            for (int j = i; j < n-i; j++) {                int x = i, y = j;                int pre = matrix[x][y];                for (int k = 0; k < 4; k++) {                    int next = matrix[y][n-x];                    matrix[y][n-x] = pre;                    int tmp = x;                    x = y;                    y = n - tmp;                    pre = next;                 }            }        }     }};