<p>Write a program to solve a Sudoku puzzle by filling the empty cells.</p>

<p>A sudoku solution must satisfy <strong>all of the following rules</strong>:</p>

<ol>
	<li>Each of the digits <code>1-9</code> must occur exactly once in each row.</li>
	<li>Each of the digits <code>1-9</code> must occur exactly once in each column.</li>
	<li>Each of the digits <code>1-9</code> must occur exactly once in each of the 9 <code>3x3</code> sub-boxes of the grid.</li>
</ol>

<p>The <code>&#39;.&#39;</code> character indicates empty cells.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png" style="height:250px; width:250px" />
<pre>
<strong>Input:</strong> board = [[&quot;5&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;],[&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;,&quot;9&quot;,&quot;5&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;],[&quot;.&quot;,&quot;9&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;],[&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;3&quot;],[&quot;4&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;],[&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;],[&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;8&quot;,&quot;.&quot;],[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;4&quot;,&quot;1&quot;,&quot;9&quot;,&quot;.&quot;,&quot;.&quot;,&quot;5&quot;],[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;9&quot;]]
<strong>Output:</strong> [[&quot;5&quot;,&quot;3&quot;,&quot;4&quot;,&quot;6&quot;,&quot;7&quot;,&quot;8&quot;,&quot;9&quot;,&quot;1&quot;,&quot;2&quot;],[&quot;6&quot;,&quot;7&quot;,&quot;2&quot;,&quot;1&quot;,&quot;9&quot;,&quot;5&quot;,&quot;3&quot;,&quot;4&quot;,&quot;8&quot;],[&quot;1&quot;,&quot;9&quot;,&quot;8&quot;,&quot;3&quot;,&quot;4&quot;,&quot;2&quot;,&quot;5&quot;,&quot;6&quot;,&quot;7&quot;],[&quot;8&quot;,&quot;5&quot;,&quot;9&quot;,&quot;7&quot;,&quot;6&quot;,&quot;1&quot;,&quot;4&quot;,&quot;2&quot;,&quot;3&quot;],[&quot;4&quot;,&quot;2&quot;,&quot;6&quot;,&quot;8&quot;,&quot;5&quot;,&quot;3&quot;,&quot;7&quot;,&quot;9&quot;,&quot;1&quot;],[&quot;7&quot;,&quot;1&quot;,&quot;3&quot;,&quot;9&quot;,&quot;2&quot;,&quot;4&quot;,&quot;8&quot;,&quot;5&quot;,&quot;6&quot;],[&quot;9&quot;,&quot;6&quot;,&quot;1&quot;,&quot;5&quot;,&quot;3&quot;,&quot;7&quot;,&quot;2&quot;,&quot;8&quot;,&quot;4&quot;],[&quot;2&quot;,&quot;8&quot;,&quot;7&quot;,&quot;4&quot;,&quot;1&quot;,&quot;9&quot;,&quot;6&quot;,&quot;3&quot;,&quot;5&quot;],[&quot;3&quot;,&quot;4&quot;,&quot;5&quot;,&quot;2&quot;,&quot;8&quot;,&quot;6&quot;,&quot;1&quot;,&quot;7&quot;,&quot;9&quot;]]
<strong>Explanation:</strong>&nbsp;The input board is shown above and the only valid solution is shown below:

<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Sudoku-by-L2G-20050714_solution.svg/250px-Sudoku-by-L2G-20050714_solution.svg.png" style="height:250px; width:250px" />
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>board.length == 9</code></li>
	<li><code>board[i].length == 9</code></li>
	<li><code>board[i][j]</code> is a digit or <code>&#39;.&#39;</code>.</li>
	<li>It is <strong>guaranteed</strong> that the input board has only one solution.</li>
</ul>

class Solution {
public:
    bool solve(vector<vector<char>>& board){

        int x=-1,y=-1;

        for(int i=0;i<9;i++){
            for(int j=0;j<9;j++){

                if(board[i][j] == '.'){
                    x=i;y=j;
                    break;
                }
            }
            if(x!=-1)break;
        }

        if(x==-1 || y==-1) return true;

        set<char> st;
        for(int i='1';i<='9';i++)st.insert(i);

        

        int ii=(x/3)*3,jj=(y/3)*3;
        cout<<ii<<" "<<jj<<" ii and jj\n";
        for(int i=ii;i<=ii+2;i++){
            for(int j=jj;j<=jj+2;j++){
                // cout<<board[i][j]<<" ";
                if(board[i][j]!='.')
                // {
                    // if(st.find(v[j][]))
                    st.erase(board[i][j]);
                // }
            }
            cout<<"\n";
        }

        for(char c : st)cout<<c<<" ";
        cout<<"\n";

        for(int j=0;j<9;j++){

            if(board[x][j]!='.' && !((j/3)*3==jj))
            st.erase(board[x][j]);

            if(board[j][y]!='.' && !((j/3)*3==ii))
            st.erase(board[j][y]);
        }
        // cout<<x<<" "<<y<<"\n";
        // for(char c : st)cout<<c<<" ";
        // cout<<"\n";
        // return 1;

        if(st.empty()) return false;

        for(char c : st){
            board[x][y]=c;
            if(solve(board)) return true;
        }
        board[x][y]='.';
        return false;
    }
    void solveSudoku(vector<vector<char>>& board) {
        solve(board);
    }
};
44828