"""
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;
}
}
}
}