LeetCode--Sudoku Solver

思路：

dfs+数独游戏规则。

数独游戏规则是：

同行同列不能有重复数字；并且每9宫内不能有重复数字

class Solution {
public:
    bool isValid(vector<vector<char> > &board, int a, int b) {
        int i,j;
        for(i = 0; i < 9; i++)
            if(i != a && board[i][b] == board[a][b])
                return false;

        for(j = 0; j < 9; j++)
            if(j != b && board[a][j] == board[a][b])
                return false;

        int x = a/3*3;
        int y = b/3*3;
        for(i = 0; i < 3; i++)
            for(j = 0; j< 3; j++)
                if(x+i != a && y+j != b && board[x+i][y+j] == board[a][b])
                    return false;
        return true;
    }
    bool solveSudokudfs(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 = 1; k <= 9; k++)
                    {
                        board[i][j] = '0' + k;
                        if(isValid(board,i,j) && solveSudokudfs(board))
                            return true;
                        board[i][j] = '.';
                    }
                    return false;
                }
            }
        return true;
    }
    void solveSudoku(vector<vector<char> > &board) {
        // Note: The Solution object is instantiated only once.
        solveSudokudfs(board);
    }
};