[leetcode] 36. Valid Sudoku

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是念 2022-08-12 08:27:16 博主文章分类：C++ ©著作权

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Description

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.

[leetcode] 36. Valid Sudoku_git

A partially filled sudoku which is valid.

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.

分析

题目的意思是：验证一个9*9的数独是否是合法的。

每遍历到一个数字，需要验证该数字在其对应的行是否合法，列是否合法，在小九宫格里面是否合法。抓住这个就行了。

代码

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        if(board.empty()){
            return false;
        }
        int n=board.size();
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                if(board[i][j]!='.'){
                    if(!isValid(board,i,j)){
                        return false;
                    }
                }
            }
        }
        return true;
    }
    bool isValid(vector<vector<char>> board,int row,int col){
        int n=board.size();
        for(int i=0;i<n;i++){
            if(board[row][col]==board[i][col]&&row!=i){
                return false;
            }
            if(board[row][col]==board[row][i]&&col!=i){
                return false;
            }
        }
        for(int i=row/3*3;i<row/3*3+3;i++){
            for(int j=col/3*3;j<col/3*3+3;j++){
                if(board[i][j]==board[row][col]&&(i!=row||j!=col)){
                    return false;
                }
            }
        }
        return true;
    }
};