[leetcode]Rotate Image

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?

CC上的原题，大概还记得，时间复杂度O(n ^ 2)，空间O(1)。

算法思路：

每一次转置相映成环的四个点。这四个点的坐标与n有关，可通过归纳法求出四个对应点的坐标关系

代码如下：

public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length == 0 ) return ;
        int n = matrix.length;
        int tem = 0;
        for(int i = 0; i < n >> 1; i++){
            for(int j = i; j < n - i - 1; j++){
                tem = matrix[i][j];
                matrix[i][j] = matrix[n - 1 - j][i];
                matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1- j];
                matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];
                matrix[j][n - 1 - i] = tem;
            }
        }
    }
}

这四个坐标的对应关系真心蛋疼.....