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
 1 class Solution {
 2 public:
 3     bool isValid(vector<vector<char> > &board, int a, int b) {
 4         int i,j;
 5         for(i = 0; i < 9; i++)
 6             if(i != a && board[i][b] == board[a][b])
 7                 return false;
 8 
 9         for(j = 0; j < 9; j++)
10             if(j != b && board[a][j] == board[a][b])
11                 return false;
12 
13         int x = a/3*3;
14         int y = b/3*3;
15         for(i = 0; i < 3; i++)
16             for(j = 0; j< 3; j++)
17                 if(x+i != a && y+j != b && board[x+i][y+j] == board[a][b])
18                     return false;
19         return true;
20     }
21     bool solveSudokudfs(vector<vector<char> > &board)
22     {
23         for(int i = 0; i < 9; i++)
24             for(int j = 0; j < 9; j++)
25             {
26                 if(board[i][j] == '.')
27                 {
28                     for(int k = 1; k <= 9; k++)
29                     {
30                         board[i][j] = '0' + k;
31                         if(isValid(board,i,j) && solveSudokudfs(board))
32                             return true;
33                         board[i][j] = '.';
34                     }
35                     return false;
36                 }
37             }
38         return true;
39     }
40     void solveSudoku(vector<vector<char> > &board) {
41         // Note: The Solution object is instantiated only once.
42         solveSudokudfs(board);
43     }
44 };