LeetCode OJ 之 Sudoku Solver（求数独）

题目：

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.

写一个程序通过填充空的单元，求解数独问题。

空单元用字符'.'填充，假定给定的数独有一个唯一的解。

A sudoku puzzle...

...and its solution numbers marked in red.

思路：

DFS

代码：

class Solution {
public:
    void solveSudoku(vector<vector<char> > &board)
    {
        isSudoku(board);
        return ;
    }
    bool isSudoku(vector<vector<char> > &board)
    {
        for(int i = 0 ; i < 9 ; i++)
        {
            for(int j = 0 ; j < 9 ; j++)
            {
                if(board[i][j] == '.')
                {
                    for(int k = 0 ; k < 9 ; k++)
                    {
                        board[i][j] = '1' + k;
                        if(isValid(board,i,j) && isSudoku(board))
                            return true;
                        board[i][j] = '.';
                    }
                    return false;
                }
            }
        }
        return true;
    }
    bool isValid(const vector<vector<char> > &board , int x , int y)
    {
        int i , j;
        for(i = 0 ; i < 9 ; i++)
        {
            if(i != x && board[i][y] == board[x][y])
                return false;
        }
        for(j = 0 ; j < 9 ; j++ )
        {
            if(j != y && board[x][j] == board[x][y])
                return false;
        }
        for(i = (x/3)*3 ; i < (x/3)*3+3 ; i++)
        {
            for(j = (y/3)*3 ; j < (y/3)*3+3 ; j++)
            {
                if(x != i && y != j && board[i][j] == board[x][y])
                    return false;
            }
        }
        return true;
    }
};