LeetCode: Transpose a Matrix

PublishedNovember 20, 2025

•1 min read

Problem:

https://leetcode.com/problems/transpose-matrix/description/

Code:

class Solution:
    def transpose(self, matrix: List[List[int]]) -> List[List[int]]:
        """
        rows<-->cols (Transpose)
        """
        return [list(row) for row in zip(*matrix)]

Key Points:

Transpose means flipping the matrix over its diagonal.
Rows become columns, and columns become rows.
Example: element at (row i, col j) moves to (row j, col i).
Python’s zip(*matrix) groups the 1st elements together, then 2nd, and so on → perfect for transposing.
list(row) is used because zip gives tuples and we want lists.
This one-liner works for any rectangular matrix (not only square).
Time: O(m*n) because every element is visited once.
Space: O(m*n) for the new transposed matrix.

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