48. Rotate Image java solutions

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?

题目大意是将矩阵做就地顺时针90度旋转。   

public class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix.length;
        if(n == 0) return;
        for(int i = 0;i < n; i++){
            for(int j = 0;j < n-i; j++){//沿着副对角线旋转一次。
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n-j-1][n-i-1];
                matrix[n-j-1][n-i-1] = tmp;
            }
        }
        
        for(int i = 0;i < n/2; i++){
            for(int j = 0;j < n; j++){//沿着中轴线，上下交换一次元素
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n-i-1][j];
                matrix[n-i-1][j] = tmp;
            }
        }
    }
}