RotateMatrixBy90DegreesClockwise.py

"""
@author Anirudh Sharma

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly.
DO NOT allocate another 2D matrix and do the rotation.

Constraints:

matrix.length == n
matrix[i].length == n
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000
"""


def rotate(matrix):
    # Special cases
    if matrix is None or len(matrix) == 0:
        return matrix
    # Order of the matrix
    N = len(matrix)
    # Traverse the matrix
    for i in range(N // 2):
        for j in range(i, N - i- 1):
            # SWap elements of each cycle in clockwise order
            temp = matrix[i][j]
            matrix[i][j] = matrix[N - 1 - j][i]
            matrix[N - 1 - j][i] = matrix[N - 1 - i][N - 1 - j]
            matrix[N - 1 - i][N - 1 - j] = matrix[j][N - 1 - i]
            matrix[j][N - 1 - i] = temp
        return matrix


if __name__ == "__main__":
    matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
    print(rotate(matrix))

    matrix = [[5, 1, 9, 11], [2, 4, 8, 10], [13, 3, 6, 7], [15, 14, 12, 16]]
    print(rotate(matrix))