Leetcode_sudoku-solver

地址：http://oj.leetcode.com/problems/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.
思路：如何验证可以参考上一条博客：http://blog.csdn.net/flyupliu/article/details/24290283
用dfs+回溯方式，不断递归查找。虽然AC了但感觉效率挺低的。

dfs另外出口要把握好，这题不好调试啊。。。出了小问题要跪很久。

参考代码：

class Solution {
public:
bool is_fill(vector<vector<char>>&board, int row, int col, char ch)
{
for(int i = 0; i<9; ++i)
{
if((i!=row && board[i][col]==ch)||(i!=col && board[row][i]==ch))
return false;
}
int left_row, left_col, right_row, right_col;
if(row % 3 ==2)
{
left_row = row-2;
right_row = row;
}
else if(row % 3 ==1)
{
left_row = row-1;
right_row = row+1;
}
else
{
left_row = row;
right_row = row+2;
}

if(col % 3 ==2)
{
right_col = col;
left_col = col-2;
}
else if(col % 3 ==1)
{
left_col = col-1;
right_col = col+1;
}
else
{
left_col = col;
right_col = col + 2;
}
for(int i = left_row; i<=right_row; ++i)
for(int j = left_col; j<=right_col; ++j)
if(i!=row && j!=col && board[i][j]==ch)
return false;
return true;
}
bool dfs(vector<vector<char>>&board, int row, int col, int left)
{
if(!left)
return true;
if(board[row][col]!='.')
{
if(row < board.size()-1 && col<board.size()-1)
return dfs(board, row, col+1, left);
else if(row < board.size()-1)
return dfs(board, row+1, 0, left);
else if(col < board.size()-1)
return dfs(board, row, col+1, left);
else
return false;
}
else
{
for(char ch = '1'; ch<='9'; ++ch)
{
if(is_fill(board, row, col, ch))
{
board[row][col]=ch;
if(row < board.size()-1 && col<board.size()-1)
{
if(dfs(board, row, col+1, left-1))
return true;
}
else if(row < board.size()-1)
{
if(dfs(board, row+1, 0, left-1))
return true;
}else if(col<board.size()-1)
{
if(dfs(board, row, col+1, left-1))
return true;
}
else if(left==1)
return true;
else
return false;
board[row][col]='.';
}
}
return false;
}
}

void solveSudoku(vector<vector<char> > &board) {
if(board.empty() || board.size()!=9)
return;
int left = 0;
for(int i = 0; i<board.size(); ++i)
{
for(int j = 0; j<board.size(); ++j)
{
if(board[i][j]=='.')
++left;
}
}
dfs(board, 0, 0, left);
}
};