55 lines
1.7 KiB
Python
55 lines
1.7 KiB
Python
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class Solution:
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def isValidSudoku(self, board: List[List[str]]) -> bool:
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#
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# NOTE: **READ THE PROBLEM DESCRIPTION ALWAYS!!**
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#
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# Even though it mentions Sudoku, it doesn't mean the
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# rules are the same as the real world. Which is the case
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# here — we need to only look at the filled cell and the rules
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# provided.
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size = len(board)
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# 1. Check if rows and cols are valid
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#
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# We can iterate both rows and cols at the same time since
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# the sudoku board has 9 rows and 9 cols
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for i in range(size):
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row = set()
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col = set()
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for j in range(size):
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# ith row check
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if board[i][j] != '.':
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if board[i][j] in row:
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return False
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row.add(board[i][j])
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# ith col check
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if board[j][i] != '.':
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if board[j][i] in col:
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return False
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col.add(board[j][i])
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# 2. Check if squares are valid
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#
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# We can do normal row * col iteration and use `// 3` to figure
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# out which square a cell belongs to
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squares = [[set(), set(), set()] for _ in range(3)]
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for i in range(size):
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for j in range(size):
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cell = board[i][j]
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if cell == '.':
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continue
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square = squares[i // 3][j // 3]
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if cell in square:
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return False
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square.add(cell)
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return True
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