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Problem Link

Approach

Rotate an n × n matrix 90 degrees clockwise in place.

Two steps:

• Transpose the matrix (swap matrix[i][j] with matrix[j][i])
• Reverse each row

This maps (i, j) to (j, n - 1 - i) as required for clockwise rotation.

Allocating a new matrix uses O(n²) extra space.

Time Complexity: O(n²)
Space Complexity: O(1)

Code

class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        n = len(matrix)

        for i in range(n):
            for j in range(i + 1, n):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]

        for row in matrix:
            row.reverse()