Valid Sudoku

1Medium

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:

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

Jnaneshwara Reddy Satti

Builder · ClearCode

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Algorithm Visualizer

O(9²)

Welcome

TEST CASE: []O(9²)

clearcode.in

Execution Trace

1import collections

3def isValidSudoku(board):

4 rows = collections.defaultdict(set)

5 cols = collections.defaultdict(set)

6 squares = collections.defaultdict(set)

8 for r in range(9):

9 for c in range(9):

10 if board[r][c] == '.':

11 continue

13 val = board[r][c]

14 if (val in rows[r] or

15 val in cols[c] or

16 val in squares[(r // 3, c // 3)]):

17 return False

19 rows[r].add(val)

20 cols[c].add(val)

21 squares[(r // 3, c // 3)].add(val)

23 return True

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