<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:
   void dfs(vector<vector<char>>&grid,int r,int c)
       {
            grid[r][c]='K';

              vector<vector<int>> dir = {{1,0},{0,1},{-1,0},{0,-1}};
               int n = grid.size();
               int m = grid[0].size();
              for(int i=0;i<4;i++)
                {
                     int adjr =r+dir[i][0];
                     int adjc = c+dir[i][1];

                     if(adjr>=0 && adjr<n && adjc>=0 && adjc<m && grid[adjr][adjc]=='O')
                       {
                           dfs(grid,adjr,adjc);
                       }
                }
       }
    void solve(vector<vector<char>>& board) {
         
            vector<vector<char>> grid = board;
              int n = board.size();
              int m = board[0].size();
          for(int i=0;i<n;i++)
            {
                  for(int j=0;j<m;j++)
                    {
                         if(i==0 || j==0 || i==n-1 || j==m-1)
                           {
                             if(grid[i][j]=='O')
                               {
                                  dfs(grid,i,j);
                               }
                           }

                    }
            }

            for(int i=0;i<n;i++)
              {
                 for(int j=0;j<m;j++)
                   {
                      if(grid[i][j]=='O')
                         grid[i][j]  = 'X';

                         if(grid[i][j]=='K')
                            grid[i][j]='O';
                   }
              }

              board = grid;
        
    }
};
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