[leetcode]Rotate Image

这种题目有了正确的方法就能简单很多。这道题目是先做对角线的交换，然后上下交换。要注意的是，如果对角线交换，等号两边的i和j肯定是交换的（m[i][j]和m[j][i]）

public class Solution {
    public void rotate(int[][] matrix) {
        int len = matrix.length;
        for (int i = 0; i < len; i++)
        {
            for (int j = 0; j < len-i; j++)
            {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[len-j-1][len-i-1];
                matrix[len-j-1][len-i-1] = tmp;
            }
        }
        for (int i = 0; i < len/2; i++)
        {
            for (int j = 0; j < len; j++)
            {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[len-i-1][j];
                matrix[len-i-1][j] = tmp;
            }
        }
    }
}