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.

class Solution {
private:
     bool search(vector<vector< char>>& board, int i, int j)
    {
        unordered_set< int> hash;
         for( int k= 0;k< 9;k++)
             if(board[i][k]!= ' . ')
                hash.insert(board[i][k]- ' 0 '); 
         for( int k= 0;k< 9;k++)
             if(board[k][j]!= ' . ')
                hash.insert(board[k][j]- ' 0 ');
         for( int x=i/ 3* 3;x<i/ 3* 3+ 3;x++)
             for( int y=j/ 3* 3;y<j/ 3* 3+ 3;y++)
                 if(board[x][y]!= ' . ')
                    hash.insert(board[x][y]- ' 0 ');        
         if(hash.size()== 9)  return  false;
        
         int newi=- 1;
         int newj=- 1;    
         for(newi= 0;newi< 9;newi++)
        {
             for(newj= 0;newj< 9;newj++)
                 if((newi!=i || newj!=j) && board[newi][newj]== ' . ')                                                                               
                {
                     for( char k= ' 1 ';k<= ' 9 ';k++)
                         if(hash.find(k- ' 0 ')==hash.end())
                        {
                            board[i][j]=k;
                             if(search(board,newi,newj))  return  true;
                        }
                    board[i][j]= ' . ';
                     return  false;
                }
        }         
         for( char k= ' 1 ';k<= ' 9 ';k++)
             if(hash.find(k- ' 0 ')==hash.end())
            {
                    board[i][j]=k;    
            }
         return  true;
    }
public:
     void solveSudoku(vector<vector< char> > &board) 
    {
         int x= 0;
         int y= 0;
         for( int i= 0;i< 9;i++)
        {
             int j;
             for(j= 0;j< 9;j++)
                 if(board[i][j]== ' . ')
                {
                    x=i;
                    y=j;
                     break;
                }
                 if(j!= 9)  break;
        }
        search(board,x,y);
    }
};