<p>You are given an <code>m x n</code> matrix <code>board</code> containing <strong>letters</strong> <code>&#39;X&#39;</code> and <code>&#39;O&#39;</code>, <strong>capture regions</strong> that are <strong>surrounded</strong>:</p>

<ul>
	<li><strong>Connect</strong>: A cell is connected to adjacent cells horizontally or vertically.</li>
	<li><strong>Region</strong>: To form a region <strong>connect every</strong> <code>&#39;O&#39;</code> cell.</li>
	<li><strong>Surround</strong>: The region is surrounded with <code>&#39;X&#39;</code> cells if you can <strong>connect the region </strong>with <code>&#39;X&#39;</code> cells and none of the region cells are on the edge of the <code>board</code>.</li>
</ul>

<p>A <strong>surrounded region is captured</strong> by replacing all <code>&#39;O&#39;</code>s with <code>&#39;X&#39;</code>s in the input matrix <code>board</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">board = [[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;O&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;O&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;X&quot;,&quot;X&quot;]]</span></p>

<p><strong>Output:</strong> <span class="example-io">[[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;X&quot;,&quot;X&quot;,&quot;X&quot;],[&quot;X&quot;,&quot;O&quot;,&quot;X&quot;,&quot;X&quot;]]</span></p>

<p><strong>Explanation:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/xogrid.jpg" style="width: 367px; height: 158px;" />
<p>In the above diagram, the bottom region is not captured because it is on the edge of the board and cannot be surrounded.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">board = [[&quot;X&quot;]]</span></p>

<p><strong>Output:</strong> <span class="example-io">[[&quot;X&quot;]]</span></p>
</div>

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

<ul>
	<li><code>m == board.length</code></li>
	<li><code>n == board[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 200</code></li>
	<li><code>board[i][j]</code> is <code>&#39;X&#39;</code> or <code>&#39;O&#39;</code>.</li>
</ul>

class Solution {
    void dfs(vector<vector<int>> &visited, vector<vector<char>>&board , int i, int j)
    {
     visited[i][j]=1;
       int n = board.size();
        int m = board[0].size();
        vector<int> delrow={-1,0,0,1};
        vector<int> delcol={0,-1,1,0};
        for(int k=0;k<4;k++)
        {
            int nrow=i+delrow[k];
            int ncol=j+delcol[k];
            if(nrow>=0 && ncol>=0 && nrow<n && ncol<m && board[nrow][ncol]=='O' && !visited[nrow][ncol])
            {
                dfs(visited,board,nrow,ncol);
            }
        }

    }
public:
    void solve(vector<vector<char>>& board) {
          int n = board.size();
        int m = board[0].size();
        vector<vector<int>> visited(board.size(),vector<int>(board[0].size(),0));
        for(int i=0;i<board.size();i++)
        {
            if(board[i][0]=='O')
            {
                dfs(visited,board,i,0);
            }
            if(board[i][m-1] == 'O'){
                 dfs(visited, board, i,m-1);
            }
        }
        for(int j=0;j<m;j++){
            if(board[0][j] == 'O'){
                dfs(visited, board, 0,j);
            }
            if(board[n-1][j] == 'O'){
                 dfs(visited, board, n-1,j);
            }
        }
        for(int i=0;i<board.size();i++)
        {
            for(int j=0;j<board[0].size();j++)
            {
                if(!visited[i][j] && board[i][j]=='O')
                {
                    board[i][j]='X';
                }
            }
        }
        
    }
};
15728