Rotate Image (in Python)

Problem

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]
]

Solution

•row의 순서를 뒤집음.

•대각선 방향으로 depth를 늘려가며 (row의 길이만큼) flip 시킴.

class Solution:
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
 
        #matrix[::] = zip(*matrix[::-1])
        #return matrix
 
        size = len(matrix)
        matrix.reverse()
 
        for r in range(size) :
            c = r + 1
            while c < size :
                matrix[r][c], matrix[c][r] = matrix[c][r], matrix[r][c]
                c += 1
        

Complexity Analysis

•Time complexity : \(O(N^2)\) is a complexity given by two inserted loops.

•Space complexity : \(O(1)\)

Source

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