Leetcode 48: Rotate Image

 

General Idea:

You need to first flip matrix upside down. Then swap elements mirror to the diagonal.

<span class="hljs-comment"> # clockwise rotate
 # first reverse up to down, then swap the symmetry 
 # 1 2 3     7 8 9     7 4 1
 # 4 5 6  => 4 5 6  => 8 5 2
 # 7 8 9     1 2 3     9 6 3</span>

 

Code

class Solution(object):
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
        matrix[:] = zip(*matrix[::-1])
        

 

Idea

Pythonic way. 

 

Code

class Solution(object):
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
        
        self.upside_down(matrix)
        self.mirror_diag(matrix)

    def upside_down(self, matrix):
        n = len(matrix)
        for i in xrange(n/2):
            for j in xrange(n):
                matrix[i][j], matrix[n-i-1][j] = matrix[n-i-1][j], matrix[i][j]

    def mirror_diag(self, matrix):
        n = len(matrix)
        for i in xrange(n):
            for j in xrange(i+1, n):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]

 

Idea

Self implement upside down and mirror.

 

Reference:

https://discuss.leetcode.com/topic/15295/seven-short-solutions-1-to-7-lines

https://discuss.leetcode.com/topic/6796/a-common-method-to-rotate-the-image/2