Given a 2d array, check if it is a valid sudoku solution.

sudoku_verifier.py

#!/usr/bin/env python3

def is_valid(board, n):
    if not sanity_check(board, n):
        return False
    # Check horizontally and vertically.
    for i in range(n):
        if (not check_sub_board(board, n, 0, n, i, i + 1)
                or not check_sub_board(board, n, i, i + 1, 0, n)):
            return False
    # Check sub-boards.
    sub = 3
    for i in range(0, n, sub):
        for j in range(0, n, sub):
            if not check_sub_board(board, n, i, i + 3, j, j + 3):
                return False
    return True


def sanity_check(board, n):
    if not board or len(board) != n:
        return False
    for row in board:
        if len(row) != n:
            return False
        for cell in row:
            if cell < 1 or cell > 9:
                return False
    return True


def check_sub_board(board, n, xs, xe, ys, ye):
    s = set()
    for i in range(xs, xe):
        for j in range(ys, ye):
            s.add(board[i][j])
    return len(s) == n;


def main():
    board =[[6, 2, 5, 9, 8, 7, 1, 4, 3],
            [9, 7, 3, 4, 6, 1, 2, 8, 5],
            [8, 1, 4, 5, 3, 2, 9, 7, 6],
            [5, 8, 6, 3, 4, 9, 7, 2, 1],
            [4, 9, 1, 7, 2, 6, 3, 5, 8],
            [7, 3, 2, 8, 1, 5, 4, 6, 9],
            [3, 4, 7, 1, 5, 8, 6, 9, 2],
            [1, 6, 8, 2, 9, 4, 5, 3, 7],
            [2, 5, 9, 6, 7, 3, 8, 1, 4]]
    print(is_valid(board, 9)) # True

    board =[[3, 2, 5, 9, 8, 7, 1, 4, 6],
            [9, 7, 3, 4, 6, 1, 2, 8, 5],
            [8, 1, 4, 5, 3, 2, 9, 7, 6],
            [5, 8, 6, 3, 4, 9, 7, 2, 1],
            [4, 9, 1, 7, 2, 6, 3, 5, 8],
            [7, 3, 2, 8, 1, 5, 4, 6, 9],
            [3, 4, 7, 1, 5, 8, 6, 9, 2],
            [1, 6, 8, 2, 9, 4, 5, 3, 7],
            [2, 5, 9, 6, 7, 3, 8, 1, 4]]
    print(is_valid(board, 9)) # False

if __name__ == '__main__':
    main()