def get_solutions(filename):
    """
    Returns the list of solutions.
    Verifies that the file containing the solutions is in the correct format.
    We expect every line to contain a string of 81 digits
    representing the solution to the puzzle.
    """
    with open(filename) as f:
        solutions = f.read().split('\n')
        for solution in solutions:
            assert len(solution) == 81
            assert solution.isdigit()

    return solutions