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题目要求：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.
分析：
参考网址：http://www.cnblogs.com/panda_lin/archive/2013/11/04/sudoku_solver.html
回溯法尝试所有解0_o
① 对于每个空位‘.‘，遍历1~9，check合理之后递归；
② check的时候，不用遍历整个数独，只需检查加入的行、列和块就足够了。
代码如下：
class Solution { public: bool isValidSudoku(vector<vector<char> > &board, int x, int y) { int row, col; // Same value in the same column? for (row = 0; row < 9; ++row) { if ((x != row) && (board[row][y] == board[x][y])) { return false; } } // Same value in the same row? for (col = 0; col < 9; ++col) { if ((y != col) && (board[x][col] == board[x][y])) { return false; } } // Same value in the 3 * 3 block it belong to? for (row = (x / 3) * 3; row < (x / 3 + 1) * 3; ++row) { for (col = (y / 3) * 3; col < (y / 3 + 1) * 3; ++col) { if ((x != row) && (y != col) && (board[row][col] == board[x][y])) { return false; } } } return true; } bool internalSolveSudoku(vector<vector<char> > &board) { for (int row = 0; row < 9; ++row) { for (int col = 0; col < 9; ++col) { if (‘.‘ == board[row][col]) { for (int i = 1; i <= 9; ++i) { board[row][col] = ‘0‘ + i; if (isValidSudoku(board, row, col)) { if (internalSolveSudoku(board)) { return true; } } board[row][col] = ‘.‘; } return false; } } } return true; } void solveSudoku(vector<vector<char> > &board) { internalSolveSudoku(board); } };
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原文地址：http://www.cnblogs.com/510602159-Yano/p/4279125.html
