LeetCode 105 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?

分析：

维持一个layer变量记录当期层，对于每一层，

四条边上相同位置元素循环赋值，这样只要维持一个临时变量即可。

public class Solution {
    public void rotate(int[][] matrix) {
        if(matrix == null || matrix.length <=1)
            return;
        int n = matrix.length;
        //一层一层旋转
        for(int layer=0; layer<n/2; layer++){
            for(int i=layer; i<n-layer-1; i++){
                //四条边上同一位置元素循环赋值
                int temp = matrix[i][layer];
                matrix[i][layer] = matrix[n-layer-1][i];
                matrix[n-layer-1][i] = matrix[n-i-1][n-layer-1];
                matrix[n-i-1][n-layer-1] = matrix[layer][n-i-1];
                matrix[layer][n-i-1] = temp;
            }
        }
    }
}