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.

Solution: back-tracking..

 1 class Solution {
 2 public:
 3     typedef vector<vector<char> > BOARDTYPE;
 4     
 5     void solveSudoku(BOARDTYPE &board) {
 6         solveSudokuRe(board, 0, 0);
 7     }
 8     
 9     bool solveSudokuRe(BOARDTYPE &board, int row, int col) {
10         getNextEmpty(board, row, col); // get next empty position [row, col]
11         if(row == 9) return true;
12         vector<bool> avail(9, true);
13         getAvailable(board, avail, row, col); // available value in row/row/box
14         for(int i = 0; i < 9; ++i) {
15             if (!avail[i]) continue;
16             board[row][col] = i + '1';
17             if (solveSudokuRe(board, row, col)) return true;
18         }
19         board[row][col] = '.';
20         return false;
21     }
22     
23     void getNextEmpty(BOARDTYPE &board, int &row, int &col) {
24         do {
25             if (board[row][col] == '.') return;
26             row = (col == 8) ? row + 1 : row;
27             col = (col + 1) % 9;
28         } while (row < 9);
29     }
30     
31     void getAvailable(BOARDTYPE &board, vector<bool> &avail, int row, int col) {
32         for (int i = 0; i < 9; ++i) {
33             if (board[row][i] != '.') avail[board[row][i]-'1'] = false;
34             if (board[i][col] != '.') avail[board[i][col]-'1'] = false;
35             int box_i = row/3*3 + i/3, box_j = col/3*3 + i%3;
36             if (board[box_i][box_j] != '.') avail[board[box_i][box_j]-'1'] = false;
37         }
38     }
39 };