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+# 36. Valid Sudoku
+
+"""
+determine if a 9 x 9 sudoku board is valid. only the filled cells need to be
+validated acording to the following rules. each row must contain the digits
+1-9 without repetition, each column must contain the digits 1-9 without
+reptition, each of the nine 3 x 3 sub-boxes of the grid must contain the
+digits 1-9 without reptition. note, a sudoku board (partially filled) could
+be valid but it is not necessarily solvable. only the filled cells need to be
+validated according to the mentioned rules.
+"""
+
+
+class Solution(object):
+ def isValidSudoku(self, board):
+ """
+ :type board: List[List[str]]
+ :rtype: bool
+ """
+ rows = [[False] * 9 for _ in range(9)]
+ cols = [[False] * 9 for _ in range(9)]
+ boxes = [[False] * 9 for _ in range(9)]
+ for i in range(9):
+ for j in range(9):
+ if board[i][j] != ".":
+ num = ord(board[i][j] - ord("1"))
+ box_idx = (i // 3) * 3 + (j // 3)
+ if rows[i][num] or cols[j][num] or boxes[box_idx][num]:
+ return False
+ rows[i][num] = cols[j][num] = boxes[box_idx][num] = True
+ return True
+
+
+if __name__ == "__main__":
+ obj = Solution()
+ b1 = [
+ ["5", "3", ".", ".", "7", ".", ".", ".", "."],
+ ["6", ".", ".", "1", "9", "5", ".", ".", "."],
+ [".", "9", "8", ".", ".", ".", ".", "6", "."],
+ ["8", ".", ".", ".", "6", ".", ".", ".", "3"],
+ ["4", ".", ".", "8", ".", "3", ".", ".", "1"],
+ ["7", ".", ".", ".", "2", ".", ".", ".", "6"],
+ [".", "6", ".", ".", ".", ".", "2", "8", "."],
+ [".", ".", ".", "4", "1", "9", ".", ".", "5"],
+ [".", ".", ".", ".", "8", ".", ".", "7", "9"],
+ ]
+ b2 = [
+ ["8", "3", ".", ".", "7", ".", ".", ".", "."],
+ ["6", ".", ".", "1", "9", "5", ".", ".", "."],
+ [".", "9", "8", ".", ".", ".", ".", "6", "."],
+ ["8", ".", ".", ".", "6", ".", ".", ".", "3"],
+ ["4", ".", ".", "8", ".", "3", ".", ".", "1"],
+ ["7", ".", ".", ".", "2", ".", ".", ".", "6"],
+ [".", "6", ".", ".", ".", ".", "2", "8", "."],
+ [".", ".", ".", "4", "1", "9", ".", ".", "5"],
+ [".", ".", ".", ".", "8", ".", ".", "7", "9"],
+ ]
+ print(obj.isValidSudoku(b1))
+ print(obj.isValidSudoku(b2))