from typing import List
"""
Transposes a square matrix.
Args:
    M (List[List]): A square matrix represented as a list of lists.
Returns:
    List[List]: The transpose of the input square matrix.
Example:
    >>> square_matrix_transpose([
    ...     [1, 2, 3, 0],
    ...     [4, 5, 6, 1],
    ...     [7, 8, 9, 2],
    ...     [1, 2, 3, 4]
    ... ])
    [[1, 4, 7, 1], [2, 5, 8, 2], [3, 6, 9, 3], [0, 1, 2, 4]]
"""

def square_matrix_transpose(M) -> List[List]:
    row = []
    T = []
    ncols = len(M[0])           # ncols is number of columns in matrix A
    for i in range(0, ncols):       
        for j in range(0, ncols):
            row.append(M[j][i])
        T.append(row)
        row = []
    return T

# Example Usage
matrix = [
    [1,2,3,0],
    [4,5,6,1],
    [7,8,9,2],
    [1,2,3,4]
]

print(square_matrix_transpose(matrix))

# Output (As a matrix)
'''           
    [[1, 4, 7, 1], 
     [2, 5, 8, 2], 
     [3, 6, 9, 3], 
     [0, 1, 2, 4]]
    
'''