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"""
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?

TESTCASES:
Input:
[]
[[1]]
[[1,2,3],[4,5,6],[7,8,9]]

Output:
[]
[[1]]
[[7,4,1],[8,5,2],[9,6,3]]


The idea was firstly transpose the matrix and then flip it symmetrically. For instance,

1  2  3             
4  5  6
7  8  9
after transpose, it will be swap(matrix[i][j], matrix[j][i])

1  4  7
2  5  8
3  6  9
Then flip the matrix horizontally. (swap(matrix[i][j], matrix[i][matrix.length-1-j])

7  4  1
8  5  2
9  6  3
"""
class Solution(object):
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
        length = len(matrix);
        for i in range(length):
            for j in range(i, length):
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
                
        for i in range(length):
            for j in range(length / 2):
                temp = matrix[i][j];
                matrix[i][j] = matrix[i][length - 1 - j];
                matrix[i][length - 1 - j] = temp; 

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