leetcode-sudoku solver

 1 class Solution {
 2 public:
 3     void solveSudoku(vector<vector<char> > &board) {
 4         dfs(board, 0, 0);
 5     }
 6     bool dfs(vector<vector<char>> &board,int i,int j)
 7     {
 8         if (j >= 9) return dfs(board,i+1,0);
 9         if (i == 9) return true;
10         if (board[i][j] == ‘.‘)
11         {
12             for (int k = 1; k <= 9; k++)
13             {
14                 board[i][j] = char(k + ‘0‘);
15                 if (isValid(board, i, j))
16                 {
17                     if (dfs(board, i, j + 1)) return true;
18                 }
19                 board[i][j] = ‘.‘;
20             }
21         }
22         else return dfs(board,i,j+1);
23         return false;
24     }
25     bool isValid(vector<vector<char>> &board,int i,int j)//在board作为参数时，有&和没&，时间效率差别非常大！！！
26     {
27         for (int k = 0; k < 9; k++)
28         {
29             if (k != j&&board[i][j] == board[i][k]) return false;
30         }
31         for (int k = 0; k < 9; k++)
32         {
33             if (k != i&&board[i][j] == board[k][j]) return false;
34         }
35         for (int row = i / 3 * 3; row < i / 3 * 3 + 3; row++)//(i,j)所在的小九宫格
36         {
37             for (int col = j / 3 * 3; col < j / 3 * 3 + 3; col++)
38             {
39                 if ((row != i || col != j) && board[i][j] == board[row][col])
40                     return false;
41             }
42         }
43         return true;
44     }
45 };