【leetcode】(python) 36. Valid Sudoku有效的数独

最新推荐文章于 2020-09-10 17:36:37 发布

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该博客讨论了如何确定9x9的数独板是否有效。内容包括问题描述、示例、题意解析和解题策略。解题思路是分别检查行、列和3x3子网格是否有重复数字，如果都没有则为有效数独。

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有效的数独

Description
Example
题目大意
解题思路
- code

Description

Valid Sudoku Medium

Determine if a 9x9 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 9 3x3 sub-boxes of the grid must contain the digits 1-9 without
repetition.

A partially filled sudoku which is valid.

The Sudoku board could be partially filled, where empty cells are filled with the character ‘.’.

Example

Example 1:

Input:
[
  ["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"]
]
Output: true

Example 2:

Input:
[
  ["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"]
]
Output: false
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.

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. The given board contain only digits
1-9 and the character ‘.’. The given board size is always 9x9.

题目大意

判断一个9x9的数独板是否有效。有效返回True,否则返回False。

解题思路

这题刚开始看感觉不好做，但其实也好做。根据数独的要求，只要行不出现重复数字，列不出现重复数字，9个3*3的子网格不出现重复数字即可。那么分别判断即可，在行、列、子网格同时没有重复数字出现就是有效的数独。

code

class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:
        return self.isValidRow(board) and self.isValidCol(board) and self.isValidNineCell(board)
        
    def isValidRow(self, board):
        n = len(board)
        for r in range(n):
            row = [x for x in board[r] if x != '.']
            if len(set(row)) != len(row):
                return False
        return True

    def isValidCol(self, board):
        n = len(board)
        for c in range(n):
            col = [board[r][c] for r in range(n) if board[r][c] != '.']
            if len(set(col)) != len(col):
                return False
        return True

    def isValidNineCell(self, board):
        n = len(board)
        for r in range(0, n, 3):
            for c in range(0, n, 3):
                cell = []
                for i in range(3):
                    for j in range(3):
                        num = board[r + i][c + j]
                        if num != '.':
                            cell.append(num)
                if len(set(cell)) != len(cell):
                    return False
        return True

回家半个月好久不刷题有点找不到感觉了。