【LeetCode热题100道】37. 解数独

用回溯法解出了所有可能的解。

class Solution {
public:
    vector<vector<vector<char>>> res;
    void solveSudoku(vector<vector<char>>& board) {

        dfs(0, board);
        board = res[0];
    }
    bool check(int num, vector<vector<char>> board)
    {
        int x = num/9;
        int y = num%9;
        for(int i = 0; i < 9; ++i)
        {
            if(i != x && board[i][y] == board[x][y])
            {
                return false;
            }
            if(i != y && board[x][i] == board[x][y])
            {
                return false;
            }
        }
        for(int i = 0; i < 3; ++i)
        {
            for(int j = 0; j < 3; ++j)
            {
                if(board[i+(x/3)*3][j+(y/3)*3] == board[x][y] && i+(x/3)*3 != x && j+(y/3)*3 != y)
                {
                    return false;
                }
            }
        }
        return true;
    }
    void dfs(int num, vector<vector<char>>& board)
    {
        if(num == 81)
        {
            res.push_back(board);
            return;
        }
        int x = num/9;
        int y = num%9;
        if(board[x][y] != '.')
        {
            dfs(num+1, board);
        }
        else
        {
            for(int i = 1; i <=9; ++i)
            {
                board[x][y] = char(i + '0');
                if(check(num, board))
                {
                    dfs(num+1, board);
                }
                board[x][y] = '.';
            }
        }
    }
};