<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 vis[210][210];
    vector<vector<char>>b;
    int rows,cols;
    int dir[4][4]={{1,0},{-1,0},{0,1},{0,-1}};
    vector<vector<pair<int,int>>>comps;
    void dfs(int i,int j,vector<pair<int,int>>&comp){
         comp.push_back({i,j});
         vis[i][j]=1;
         if(i+1<rows and !vis[i+1][j] and b[i+1][j]=='O')
         dfs(i+1,j,comp);
         if(i-1>=0 and !vis[i-1][j] and b[i-1][j]=='O')
         dfs(i-1,j,comp);
         if(j+1<cols and !vis[i][j+1] and b[i][j+1]=='O')
         dfs(i,j+1,comp);
         if(j-1>=0 and !vis[i][j-1] and b[i][j-1]=='O')
         dfs(i,j-1,comp);
    }

    void solve(vector<vector<char>>& board) {
        b=board;
        memset(vis,0,sizeof(vis));
        rows=board.size();
        cols=board[0].size();
        for(int i=0;i<rows;i++){
            for(int j=0;j<cols;j++){
                if(board[i][j]=='O' and !vis[i][j]){
                    vector<pair<int,int>>comp;
                    dfs(i,j,comp);
                    comps.push_back(comp);
                }
            }
        }
        bool y=0;
        for(auto comp:comps){
            y=0;
            for(auto [i,j]:comp){
                if(i==0 || i==rows-1 || j==0 || j==cols-1){
                    y=1;break;
                }
            }
            if(y)continue;
            else{
            for(auto [i,j]:comp){
                board[i][j]='X';    
            }
            }
        }
    }
};
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