Program to rotate square matrix by 90 degrees counterclockwise in Python

Python Server Side Programming Programming

Suppose we have a square matrix, we have to rotate it 90 degrees counter-clockwise.

1	4	7
2	5	8
3	6	9

then the output will be

7	8	9
4	5	6
1	2	3

To solve this, we will follow these steps −

if matrix is empty, then
- return a blank list
n := row count of matrix
for each row in matrix, do
- reverse the row
for i in range 0 to n−1, do
- for j in range 0 to i−1, do
  - swap matrix[i, j] and matrix[j, i]
return matrix

Let us see the following implementation to get better understanding −

Example

Live Demo

class Solution:
   def solve(self, matrix):
      if not matrix or not matrix[0]:
         return []
      n = len(matrix)
      for row in matrix:
         row.reverse()
      for i in range(n):
         for j in range(i):
            matrix[i][j], matrix[j][i] = matrix[j][i],
            matrix[i][j]
      return matrix
ob = Solution()
matrix = [
[1, 4, 7],
[2, 5, 8],
[3, 6, 9]
]
print(ob.solve(matrix))

Input

[
[1, 4, 7],
[2, 5, 8],
[3, 6, 9] ]

Output

[
[7, 8, 9],
[4, 5, 6],
[1, 2, 3]]

Arnab Chakraborty

Published on 21-Oct-2020 10:30:29

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