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?

 

可以找规律 得出映射关系，（i,j）===>(j,n-1-j)

由于要in-place，不能直接新建矩阵，所以从外圈开始，一个个置换。

public class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix[0].length -1;
        for(int i = 0;i <= n - i;i++){
            for(int j = i;j <= n - i - 1;j++)
            {
                int tmp = matrix[j][n-i];
                matrix[j][n-i] = matrix[i][j];
                matrix[i][j] = matrix[n-j][i];
                matrix[n-j][i] = matrix[n-i][n-j];
                matrix[n-i][n-j] = tmp;
            }
        }
    }
}