【題目】

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

【題意】

解數獨

【思路】

【程式碼】

class Solution {
public:
    bool isValid(vector<vector<char> > &board, int i, int j){
        //判斷所在行
        for(int col=0; col<9; col++){
            if(col!=j && board[i][j]==board[i][col])return false;
        }
        //判斷所在列
        for(int row=0; row<9; row++){
            if(row!=i && board[i][j]==board[row][j])return false;
        }
        //判斷所在block
        int x=i/3*3;
        int y=j/3*3;
        for(int row=x; row<x+3; row++){
            for(int col=y; col<y+3; col++){
                if(row!=i && col!=j && board[i][j]==board[row][col])return false;
            }
        }
        return true;
    }
    
    bool sodoku(vector<vector<char> > &board){
        for(int i=0; i<9; i++){
            for(int j=0; j<9; j++){
                if(board[i][j]=='.'){
                    for(int value=1; value<=9; value++){
                        board[i][j]='0'+value;
                        if(isValid(board, i, j)&&sodoku(board))return true;
                        board[i][j]='.';
                    }
                    return false;
                }
            }
        }
        return true;
    }

    void solveSudoku(vector<vector<char> > &board) {
        sodoku(board);    
    }
};