def determinant(matrix: list[list[int]]) -> int:
    det = 0
    match ln := len(matrix):
        case 1:
            return matrix[0][0]
        case 2:
            return matrix[0][0] * matrix[1][1] - matrix[0][1] * matrix[1][0]
        case _:
            for k in range(ln):
                det += matrix[0][k] * (-1) ** k * determinant([matrix[i][:k] + matrix[i][k+1:] for i in range(1,ln)])
    return det


a = [[1, 2, 9],
     [4, 5 ,6],
     [7, 8, 9]]

print(determinant(a))