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57 lines
2.2 KiB
Plaintext
57 lines
2.2 KiB
Plaintext
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---
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title: '36. Valid Sudoku'
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description: 'Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:'
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icon: dot
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topics:
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- { name: "Array", slug: "array" }
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- { name: "Hash Table", slug: "hash-table" }
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- { name: "Matrix", slug: "matrix" }
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issue: "https://github.com/prdlk/leetcode/issues/94"
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sidebar:
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label: 'Valid Sudoku'
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badge: 'Medium'
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---
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### Example 1:
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- Input: `board = [["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"]]`
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- Output: `true`
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### Example 2:
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- Input: `board = [["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"]]`
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- Output: `false`
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- Explanation: Same as Example `1`, except with the `5` in the top left corner being modified to `8`. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
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### Constraints:
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- `board.length == 9`
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- `board[i].length == 9`
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- board[i][j] is a digit 1-9 or '.'.
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## Solution
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```py
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import collections
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class Solution:
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def isValidSudoku(self, board: list[list[str]]) -> bool:
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cols = collections.defaultdict(set)
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rows = collections.defaultdict(set)
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squares = collections.defaultdict(set) # (r/3, c/3)
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for r in range(9):
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for c in range(9):
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if board[r][c] == ".":
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continue
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if (
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board[r][c] in rows[r]
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or board[r][c] in cols[c]
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or board[r][c] in squares[(r // 3, c // 3)]
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):
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return False
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cols[c].add(board[r][c])
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rows[r].add(board[r][c])
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squares[(r // 3, c // 3)].add(board[r][c])
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return True
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```
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