Rotates an N x N matrix M 90 degrees clockwise.

matrix_rotate.py

class Matrix:

	@staticmethod
	def rotate(m, n):
		"""Rotates a matrix m of n x n size"""
		
		# reverse each row of the matrix
		for i in range(n):
			m[i] = m[i][::-1]

		# swap in place
		src_col = n - 1
		for i in range(n):
			dest_col = 0
			for j in range(n-1, -1, -1):
				if i == j and src_col == dest_col:
					break
				else:
					# swap the elements
					m[i][dest_col], m[j][src_col] = m[j][src_col], m[i][dest_col]
				dest_col += 1

			src_col -= 1

		return m

import unittest
class TestMatrix(unittest.TestCase):
	
	def test_two_by_two(self):
		M = [
		[1, 2],
		[3, 4]]
		n = 2
		R = [
		[3, 1],
		[4, 2]]
		self.assertEqual(Matrix.rotate(M, n), R)

	def test_three_by_three(self):
		M = [
		[1,2,3],
		[4,5,6],
		[7,8,9]]
		n = 3
		R = [
		[7, 4, 1],
		[8, 5, 2],
		[9, 6, 3]]
		self.assertEqual(Matrix.rotate(M, n), R)

	def test_four_by_four(self):
		M = [
		[1,   2,  3,  4],
		[5,   6,  7,  8],
		[9,  10, 11, 12],
		[13, 14, 15, 16]]
		n = 4
		R = [
		[13,  9, 5, 1],
		[14, 10, 6, 2],
		[15, 11, 7, 3],
		[16, 12, 8, 4]]
		self.assertEqual(Matrix.rotate(M, n), R)


if __name__ == '__main__':
 	unittest.main()