[Leetcode] 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.

A sudoku puzzle...

 

...and its solution numbers marked in red.

 

暴力DFS！

 1 class Solution {

 2 public:

 3     bool isValid(vector<vector<char> > &board, int a, int b) {

 4         for (int i = 0; i < 9; ++i) {

 5             if (i != a && board[i][b] == board[a][b])

 6                 return false;

 7         }

 8         for (int j = 0; j < 9; ++j) {

 9             if (j != b && board[a][j] == board[a][b])

10                 return false;

11         }

12         int x = a / 3 * 3, y = b / 3 * 3;

13         for (int i = 0; i < 3; ++i) {

14             for (int j = 0; j < 3; ++j) {

15                 if (x + i != a && y + j != b && board[x + i][y + j] == board[a][b])

16                     return false;

17             }

18         }

19         return true;

20     }

21     

22     bool solveHelper(vector<vector<char> > &board) {

23         for (int i = 0; i < 9; ++i) {

24             for (int j = 0; j < 9; ++j) {

25                 if (board[i][j] == '.') {

26                     for (int k = 1; k <= 9; ++k) {

27                         board[i][j] = '0' + k;

28                         if (isValid(board, i, j) && solveHelper(board)) {

29                             return true;

30                         }

31                         board[i][j] = '.';

32                     }

33                     return false;

34                 }

35             }

36         }

37         return true;

38     }

39     

40     void solveSudoku(vector<vector<char> > &board) {

41         solveHelper(board);

42     }

43 };