Daily LeetCode 36. Valid Sudoku

https://leetcode.com/problems/valid-sudoku/

Medium

问题描述

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

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

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.

思路及代码：

这一题是今天早上算法课的测试中做到的题目

数独有三条规则：

1. 每一行都由1～9组成，互不重复
2. 每一列都有1～9组成，互不重复
3. 每一个小的九宫格，也都由1～9组成，互不重复

我们只需要按照这三条规则，对给定的数独进行判断，看该数独是不是符合规则。

我们通过set()方法来判断是否存在重复元素

class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:
        if board is None or len(board) != 9 or len(board[0]) != 9:
            return False

        for i in range(9):
            row = [_ for _ in board[i] if _ != '.']
            if len(row) != len(set(row)):
                return False

        for i in range(9):
            col = [board[_][i] for _ in range(9) if board[_][i] != '.']
            if len(col) != len(set(col)):
                return False

        for i in range(0, 9, 3):
            for j in range(0, 9, 3):
                cell = []
                for k in range(3):
                    for p in range(3):
                        num = board[i + k][j + p]
                        if num != '.':
                            cell.append(num)
                if len(cell) != len(set(cell)):
                    return False

        return True