Problem

Given a 2D array of integers, write a function that determines whether the array is a valid Sudoku board. A Sudoku board is valid if:
- Each row contains exactly 9 integers
- Each column contains exactly 9 integers
- Each 3x3 subarray (indicated by bold lines in the array below) contains exactly 9 integers
Input: 
[[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]]
Output: true

Solution

def is_valid_sudoku(board):
    # check rows
    for row in board:
        if not is_valid_row(row):
            return False
    # check columns
    for i in range(len(board)):
        column = [row[i] for row in board]
        if not is_valid_row(column):
            return False
    # check 3x3 subarrays
    for i in range(0, len(board), 3):
        for j in range(0, len(board), 3):
            subarray = [board[i][j], board[i][j+1], board[i][j+2], board[i+1][j], board[i+1][j+1], board[i+1][j+2], board[i+2][j], board[i+2][j+1], board[i+2][j+2]]
            if not is_valid_row(subarray):
                return False
    return True

def is_valid_row(row):
    return len(row) == 9 and len(set(row)) == 9 and all(0 < x < 10 for x in row)

board = [[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]]

print(is_valid_sudoku(board))