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[48] Rotate Image

https://leetcode.com/problems/rotate-image/description/

algorithms
Medium (45.08%)
Source Code: 48.rotate-image.py
Total Accepted: 240.3K
Total Submissions: 502.9K
Testcase Example: '[[1,2,3],[4,5,6],[7,8,9]]'

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] ]

python

class Solution(object):
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: None Do not return anything, modify matrix in-place instead.
        """
        if not matrix or not matrix[0]: return

        m, n = len(matrix), len(matrix[0])

        for i in range(m):
            for j in range(0, i):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]

        for i in range(m):
            for j in range(n/2):
                matrix[i][j], matrix[i][n-1-j] = matrix[i][n-1-j], matrix[i][j]