Rotate Image

Rotate Image 

问题：

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?

思路：

　　画画图就知道该怎么样替换了

我的代码：

public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0)   return;
        int n = matrix.length;
        for(int i = 0; i < n/2; i++)
        {
            for(int j = i; j < n - i - 1; j++)
            {
                int first = matrix[i][j];
                matrix[i][j] = matrix[n-j-1][i];
                matrix[n-j-1][i] = matrix[n-i-1][n-j-1];
                matrix[n-i-1][n-j-1] = matrix[j][n-i-1];
                matrix[j][n-i-1] = first;
            }
        }
        return;
    }
}

学习之处：

　　swap方法的扩展，按照这样的替换方法 tmp = A ; A = B ; B = C; C = D; D=tmp;