Algorithm to check if a sudoku solution is valid

sudoku_checker.py

from __future__ import print_function, division

def check_sudoku(arr):
    # 9 rows, 9 columns and 9 sub squares
    # Each of them need to have all the digits
    # Not using bit shifting 
    alignments = [987654321] * 27
    
    for i, row in enumerate(arr):
        for j, x in enumerate(row):
            if x == 0:
                return False
            n = x * pow(10, x - 1)
            alignments[i] -= n
            alignments[9 + j] -= n
            alignments[18 + i // 3 * 3 + j // 3] -= n
    return sum(alignments) == 0


test_arr = [[5, 3, 4, 6, 7, 8, 9, 1, 2], [6, 7, 2, 1, 9, 5, 3, 4, 8], [1, 9, 8, 3, 4, 2, 5, 6, 7],
            [8, 5, 9, 7, 6, 1, 4, 2, 3], [4, 2, 6, 8, 5,
                                          3, 7, 9, 1], [7, 1, 3, 9, 2, 4, 8, 5, 6],
            [9, 6, 1, 5, 3, 7, 2, 8, 4], [2, 8, 7, 4, 1, 9, 6, 3, 5], [3, 4, 5, 2, 8, 6, 1, 7, 9]]
check_sudoku(test_arr)