Array - 36. Valid Sudoku

#===================================
# Tanzila Islam
# Email: tanzilamohita@gmail.com
# Language: Python 3
#===================================

class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:
        # 1. Each row must contain the digits 1-9 without repetition.

        # row
        for row in range(9):
            dig_arr = [0] * 10
            for col in range(9):
                if board[row][col].isdigit():
                    num = int(board[row][col])
                    if dig_arr[num] == 0:
                        dig_arr[num] = 1
                    else:
                        return 0

        # 2. Each column must contain the digits 1-9 without repetition.

        # column
        for col in range(9):
            dig_arr = [0] * 10
            for row in range(9):
                if board[row][col].isdigit():
                    num = int(board[row][col])
                    if dig_arr[num] == 0:
                        dig_arr[num] = 1
                    else:
                        return 0

        # 3. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. 

        # sub-boxes
        for row in range(0, 9, 3):
            for col in range(0, 9, 3):
                dig_arr = [0] * 10
                for i in range(row, row+3):
                    for j in range(col, col+3):
                        if board[i][j].isdigit():
                            num = int(board[i][j])
                            if dig_arr[num] == 0:
                                dig_arr[num] = 1
                            else:
                                return 0
        
        return 1