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94 lines
2.6 KiB
Python
94 lines
2.6 KiB
Python
"""
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36. Valid Sudoku
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Difficulty: Medium
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https://leetcode.com/problems/valid-sudoku/
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──────────────────────────────────────────────────
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Determine if a 9 x 9 Sudoku board is valid. Only the filled cells
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need to be validated according to the following rules:
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• Each row must contain the digits 1-9 without repetition.
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• Each column must contain the digits 1-9 without repetition.
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• Each of the nine 3 x 3 sub-boxes of the grid must contain the
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digits 1-9 without repetition.
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Note:
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• A Sudoku board (partially filled) could be valid but is not
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necessarily solvable.
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• Only the filled cells need to be validated according to the
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mentioned rules.
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Example 1:
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Input: board =
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[["5","3",".",".","7",".",".",".","."]
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,["6",".",".","1","9","5",".",".","."]
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,[".","9","8",".",".",".",".","6","."]
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,["8",".",".",".","6",".",".",".","3"]
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,["4",".",".","8",".","3",".",".","1"]
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,["7",".",".",".","2",".",".",".","6"]
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,[".","6",".",".",".",".","2","8","."]
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,[".",".",".","4","1","9",".",".","5"]
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,[".",".",".",".","8",".",".","7","9"]]
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Output: true
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Example 2:
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Input: board =
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[["8","3",".",".","7",".",".",".","."]
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,["6",".",".","1","9","5",".",".","."]
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,[".","9","8",".",".",".",".","6","."]
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,["8",".",".",".","6",".",".",".","3"]
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,["4",".",".","8",".","3",".",".","1"]
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,["7",".",".",".","2",".",".",".","6"]
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,[".","6",".",".",".",".","2","8","."]
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,[".",".",".","4","1","9",".",".","5"]
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,[".",".",".",".","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
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corner being modified to 8. Since there are two 8's in the top left
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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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"""
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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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