<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(int row, int col, vector<vector<int>> &vis,vector<vector<char>> &mat,vector<int>delrow, vector<int>delcol) {
        vis[row][col] = 1; 
        int n = mat.size();
        int m = mat[0].size();
        for(int i = 0;i<4;i++) {
            int nrow = row + delrow[i];
            int ncol = col + delcol[i]; 
            if(nrow >=0 && nrow <n && ncol >= 0 && ncol < m 
          && mat[nrow][ncol] == 'O'  && !vis[nrow][ncol] ){
                dfs(nrow, ncol, vis, mat, delrow, delcol); 
            }
        }
    }
    void solve(vector<vector<char>>& mat) {
        
        int n = mat.size();
        int m = mat[0].size();
        vector<int>delrow = {-1, 0, +1, 0};
        vector<int>delcol = {0, 1, 0, -1}; 
        vector<vector<int>> vis(n, vector<int>(m,0)); 

        for(int j = 0 ; j<m;j++) {
       
            if(!vis[0][j] && mat[0][j] == 'O') {
                dfs(0, j, vis, mat, delrow, delcol); 
            }
           
            if(!vis[n-1][j] && mat[n-1][j] == 'O') {
                dfs(n-1,j,vis,mat,delrow, delcol); 
            }
        }
        for(int i = 0;i<n;i++){
            
            if(!vis[i][0] && mat[i][0] == 'O') {
                dfs(i, 0, vis, mat, delrow, delcol); 
            }
           
            if(!vis[i][m-1] && mat[i][m-1] == 'O') {
                dfs(i, m-1, vis, mat, delrow, delcol); 
            }
        }

        for(int i = 0;i<n;i++) {
            for(int j= 0 ;j<m;j++) {
                if(!vis[i][j] && mat[i][j] == 'O') 
                    mat[i][j] = 'X'; 
            }
        }
    }
};
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