037 Sudoku Solver 解数独

写一个程序通过填充空格来解决数独。空格用 '.' 表示。

详见：https://leetcode.com/problems/sudoku-solver/description/

class Solution {
public:
    bool solveSudoku(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) && solveSudoku(board))
                            return true;
                        board[i][j] = '.';
                    }
                    return false;
                }
            }
        return true;
    }

    bool isValid(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 = 3 * (x / 3); i < 3 * (x / 3 + 1); i++)
            for (j = 3 * (y / 3); j < 3 * (y / 3 + 1); j++)
                if (i != x && j != y && board[i][j] == board[x][y])
                    return false;
        return true;
    }
};