标签：style blog http io color ar for sp div
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.
终于到了朝思暮想的sudoku solver了， 有了Valid Sudoku的基础，我知道了用哈希表可以很方便的判断冲突。思路还是遍历这个board，这次是找到为空的位置，然后对可能的结果集进行筛选：把行、列、3x3出现的数字都去掉，剩下的就是可能的结果集。然后把结果集里的元素一个一个拿出来进行深度搜索，直到满足递归出口：row == 8 && col == 8 说明board遍历完毕，得到结果； 如果函数最终返回却没有满足那个条件的话，就说明此局无解。
在解此题时主要遇到的问题是对递归出口判断的模棱两可，还有传board的时候我老是喜欢传个引用，导致一次深搜改变了board。。这是个bug，在word breakII时也遇到过。总值对此题的理解还需深入，继续推敲。
1 void solver(vector<vector<char>> board, int row, int col, vector<vector<char>> &ret) { 2 if (board[row][col] != ‘.‘) { 3 if (row == 8 && col == 8) { 4 ret = board; 5 return; 6 } 7 else if (++col >= 9) { 8 ++row; 9 col = 0; 10 } 11 solver(board, row, col, ret); 12 return; 13 } 14 15 // calculate solve space 16 unordered_set<char> set = preset; 17 // filter colum 18 for (int k = 0; k < 9; k++) { 19 char searched = board[k][col]; 20 if (searched != ‘.‘ && set.find(searched) != set.end()) { 21 set.erase(searched); 22 } 23 } 24 // filter row 25 for (int k = 0; k < 9; k++) { 26 char searched = board[row][k]; 27 if (searched != ‘.‘ && set.find(searched) != set.end()) { 28 set.erase(searched); 29 } 30 } 31 // filter 3*3 32 int square_row_offset = row / 3; 33 int square_col_offset = col / 3; 34 for (int k = square_row_offset * 3; k < square_row_offset * 3 + 3; k++) { 35 for (int l = square_col_offset * 3; l < square_col_offset * 3 + 3; l++) { 36 char searched = board[k][l]; 37 if (searched != ‘.‘ && set.find(searched) != set.end()) { 38 set.erase(searched); 39 } 40 } 41 } 42 43 for (char ele: set) { 44 board[row][col] = ele; 45 46 if (row == 8 && col == 8) { 47 ret = board; 48 return; 49 } 50 51 solver(board, row, col+1, ret); 52 } 53 } 54 55 56 vector<vector<char>> sudokuSolver(vector<vector<char>> &board) { 57 vector<vector<char>> ret; 58 solver(board, 0, 0, ret); 59 return ret; 60 }
标签：style blog http io color ar for sp div
原文地址：http://www.cnblogs.com/agentgamer/p/4072751.html
