<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:
    
    int dx[4]={0,0,-1,1};
    int dy[4]={-1,1,0,0};
    void Fun(vector<vector<char>>&board,int i,int j,int n,int m,vector<vector<int>>&vis,int &flag){
       
       for(int k=0;k<4;k++){
        int row=i+dx[k];
        int col=j+dy[k];
        if(row>=0 && col>=0 && row<n && col<m && vis[row][col]==0 && board[row][col]=='O'){
            vis[row][col]=1;
            if(flag==1){
                board[row][col]='X';
            }
            Fun(board,row,col,n,m,vis,flag);
        }
       }
       return ;
    }
    void solve(vector<vector<char>>& board) {
        int n=board.size();
        int m=board[0].size();
        int flag=0;
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(int i=0;i<m;i++){
           if(vis[0][i]==0 && board[0][i]=='O'){
            vis[0][i]=1;
            Fun(board,0,i,n,m,vis,flag);
           }
           if(vis[n-1][i]==0 && board[n-1][i]=='O'){
            vis[n-1][i]=1;
            Fun(board,n-1,i,n,m,vis,flag);
           }
        }
        for(int i=0;i<n;i++){
            if(vis[i][0]==0 && board[i][0]=='O'){
               vis[i][0]=1;
               Fun(board,i,0,n,m,vis,flag);
            }
            if(vis[i][m-1]==0 && board[i][m-1]=='O'){
                vis[i][m-1]=1;
                Fun(board,i,m-1,n,m,vis,flag);
            }
        }
        flag=1;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(vis[i][j]==0 && board[i][j]=='O'){
                    vis[i][j]=1;
                    board[i][j]='X';
                    Fun(board,i,j,n,m,vis,flag);
                }
            }
        }
        
    }
};
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