#36

Valid Sudoku

medium· Arrays & Hashingruns: 0

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated. Each row, each column, and each of the nine 3x3 sub-boxes must contain the digits 1 to 9 without repetition. Empty cells are marked with '.'.

wpm 0acc 100%time 0:000 / 639

from collections import defaultdict

class Solution:
    def isValidSudoku(self, board: list[list[str]]) -> bool:
        rows = defaultdict(set)
        cols = defaultdict(set)
        boxes = defaultdict(set)
        for r in range(9):
            for c in range(9):
                cell = board[r][c]
                if cell == ".":
                    continue
                box = (r // 3, c // 3)
                if cell in rows[r] or cell in cols[c] or cell in boxes[box]:
                    return False
                rows[r].add(cell)
                cols[c].add(cell)
                boxes[box].add(cell)
        return True

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