LeetCode Online Judge 题目C# 练习 - Sudoku Solver

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.

 1         public static void SudokuSolver(List<List<char>> board)
 2         {
 3             solver(board);
 4         }
 5 
 6         public static bool solver(List<List<char>> board)
 7         {
 8             for (int r = 0; r < 9; r++)
 9             {
10                 for (int c = 0; c < 9; c++)
11                 {
12                     if (board[r][c] == '.')
13                     {
14                         for (int k = 1; k <= 9; k++)
15                         {
16                             board[r][c] = Convert.ToChar('0' + k);
17                             if (isValid(board, r, c))
18                             {
19                                 if(solver(board))
20                                     return true;
21                             }
22                             board[r][c] = '.';
23                         }
24                         return false;
25                     }
26                 }
27             }
28             return true;
29         }
30 
31         public static bool isValid(List<List<char>> board, int r, int c)
32         {
33             //////////////CHECK ROW/////////////////////
34             bool[] Row = new bool[9];
35             for (int i = 0; i < 9; i++)
36             {
37                 if (board[r][i] >= '1' && board[r][i] <= '9')
38                 {
39                     if (Row[board[r][i] - '1'] == false)
40                         Row[board[r][i] - '1'] = true;
41                     else
42                         return false;
43                 }
44             }
45 
46             /////////////CHECK COLUMN//////////////////
47             bool[] Col = new bool[9];
48             for (int i = 0; i < 9; i++)
49             {
50                 if (board[i][c] >= '1' && board[i][c] <= '9')
51                 {
52                     if (Col[board[i][c] - '1'] == false)
53                         Col[board[i][c] - '1'] = true;
54                     else
55                         return false;
56                 }
57             }
58 
59             /////////////CHECK GRID///////////////////
60             bool[] Grid = new bool[9];
61             // r / 3 * 3 = beginning row number of that grid
62             // c / 3 * 3 = beginning column number of that grid
63             for (int i = (r / 3) * 3; i < (r / 3) * 3 + 3; i++)
64             {
65                 for (int j = (c / 3) * 3; j < (c / 3) * 3 + 3; j++)
66                 {
67                     if (board[i][j] >= '1' && board[i][j] <= '9')
68                     {
69                         if (Grid[board[i][j] - '1'] == false)
70                             Grid[board[i][j] - '1'] = true;
71                         else
72                             return false;
73                     }
74                 }
75             }
76 
77             return true;
78         }

代码分析：

　　递归，就是每个数字试，检查行列格子都Valid就递归到下一个，如果不Valid记得要把当前数字归空（ '.' ），因为这这个格子有可能0～9都不Valid，需要回溯到前一个格子。DP有点不知道怎么弄。

　　我也有个Follow Up, 如果要打印所有可能的解。该怎么写呢？

posted @ 2012-10-19 00:07  ETCOW  阅读(401)  评论(0)  编辑  收藏  举报