36. valid sudoku

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

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

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

solution

For each row, column, and square, check for valid state.

def isValidSudoku(self, board: List[List[str]]) -> bool:
	def is_valid_row(i):
		filtered = list(filter(lambda x: x != ".", board[i]))
		return len(filtered) == len(set(filtered))
	  
	def is_valid_col(j):
		col = [row[j] for row in board]
		filtered = list(filter(lambda x: x != ".", col))
		return len(filtered) == len(set(filtered))
	  
	def is_valid_square(r, c):
		seen = set()
		for i in range(r*3, r*3+3):
			for j in range(c*3, c*3+3):
				if board[i][j] != ".":
					if board[i][j] in seen:
						return False
					seen.add(board[i][j])
		return True
 
	m, n = len(board), len(board[0])
	valid = True
	for i in range(m):
		valid = valid and is_valid_row(i)
	for j in range(n):
		valid = valid and is_valid_col(j)
	for r in range(3):
		for c in range(3):
			valid = valid and is_valid_square(r, c)
	return valid