rotate-image.py

# -*- coding:utf-8 -*-


# You are given an n x n 2D matrix representing an image.
#
# Rotate the image by 90 degrees (clockwise).
#
# Note:
#
# 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.
#
# Example 1:
#
#
# Given input matrix = 
# [
#   [1,2,3],
#   [4,5,6],
#   [7,8,9]
# ],
#
# rotate the input matrix in-place such that it becomes:
# [
#   [7,4,1],
#   [8,5,2],
#   [9,6,3]
# ]
#
#
# Example 2:
#
#
# Given input matrix =
# [
#   [ 5, 1, 9,11],
#   [ 2, 4, 8,10],
#   [13, 3, 6, 7],
#   [15,14,12,16]
# ], 
#
# rotate the input matrix in-place such that it becomes:
# [
#   [15,13, 2, 5],
#   [14, 3, 4, 1],
#   [12, 6, 8, 9],
#   [16, 7,10,11]
# ]
#
#


class Solution(object):
    def rotate(self, matrix):
        n = len(matrix)
        for l in xrange(n / 2):
            r = n - 1 - l
            for p in xrange(l, r):
                q = n - 1 - p
                cache = matrix[l][p]
                matrix[l][p] = matrix[q][l]
                matrix[q][l] = matrix[r][q]
                matrix[r][q] = matrix[p][r]
                matrix[p][r] = cache