LeetCode OJ：Sudoku Solver（数独游戏）

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character ‘.‘.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

dfs,一直寻找，不行返回即可：

 1 class Solution {
 2 public:
 3     void solveSudoku(vector<vector<char>>& board) {
 4         doSudoku(board);
 5     }
 6
 7     bool checkValid(vector<vector<char>>&board, int x, int y)
 8     {
 9         for(int i = 0; i < 9; i++){
10             if(i!=x)
11                 if(board[i][y] == board[x][y]) return false;
12         }
13
14         for(int j = 0; j < 9; j++){
15             if(j != y)
16                 if(board[x][j] == board[x][y]) return false;
17         }
18
19         for(int i = (x/3) * 3; i < (x/3 + 1) * 3; ++i){
20             for(int j = (y/3) * 3; j < (y/3 + 1) * 3; ++j){
21                 if((i!=x) || (j != y))
22                     if(board[x][y] == board[i][j]) return false;
23             }
24         }
25         return true;
26     }
27
28     bool doSudoku(vector<vector<char>> & board)
29     {
30         for(int row = 0; row < 9; ++row){
31             for(int col = 0; col < 9; ++col){
32                 if(board[row][col] == ‘.‘){
33                     for(int i = 1; i <= 9; ++i){
34                         board[row][col] = ‘0‘ + i;
35                         if(checkValid(board, row, col)){
36                             if(doSudoku(board)){
37                                 return true;
38                             }
39                         }
40                         board[row][col] = ‘.‘;
41                     }
42                     return false;
43                 }
44             }
45         }
46         return true;
47     }
48 };