<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 {
public:
    bool isSorrounded(vector<vector<char>>& b,vector<vector<int>>& vis,int i,int j,int r ,int c)
    {
      if(i>=r||i<0||j>=c||j<0) return false;
      if(vis[i][j]==1||b[i][j]=='X') return true;
      vis[i][j]=1;
      bool f= isSorrounded(b,vis, i+1, j, r , c);
      f=isSorrounded(b,vis, i, j+1, r , c)&&f;
      f=isSorrounded(b,vis, i-1, j, r , c)&&f;
      f=isSorrounded(b,vis, i, j-1, r , c)&&f;
      return f;
    }
        void doX(vector<vector<char>>& b,vector<vector<int>>& vis,int i,int j,int r ,int c)
    {
      if(i>=r||i<0||j>=c||j<0) return ;
      if(vis[i][j]!=-1||b[i][j]=='X') return ;
       vis[i][j]=1;
       b[i][j]='X';
       doX(b,vis, i+1, j, r , c);
       doX(b,vis, i, j+1, r , c);
       doX(b,vis, i-1, j, r , c);
       doX(b,vis, i, j-1, r , c);
       return ;
    }
    void solve(vector<vector<char>>& b) {
      int r=b.size(),c=b[0].size(); 
      vector<vector<int>>vis(r,vector<int>(c,-1)); 
      for(int i=0;i<r;i++)
      {
        for(int j=0;j<c;j++)
        {
          if(b[i][j]=='O'&&vis[i][j]==-1)
          {
            //call bfs to find is sorunded or not
            bool f= isSorrounded(b,vis, i, j, r , c);

            if(f){
                  vector<vector<int>>vis2(r,vector<int>(c,-1)); 
                  doX(b,vis2, i, j, r , c);
            }
 
          }
        }
      }
    }
};
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