<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 bfs1(vector<vector<char>>& board,vector<vector<int>>& vis,int i,int j){
        int n = board.size();
        int m = board[0].size();
        vis[i][j] = 1;
        vector<pair<int,int>>direction{{-1,0},{1,0},{0,1},{0,-1}};
        queue<pair<int,int>>q;
        q.push({i,j});
        while(!q.empty()){
            int size = q.size();
            while(size--){
                auto [xd,yd] = q.front();
                q.pop();
                for(auto direc:direction){
                    int nx = xd + direc.first;
                    int ny = yd + direc.second;
                    if(nx>=0 && nx<n && ny>=0 && ny<m && (board[nx][ny]=='O') && !vis[nx][ny]){
                        vis[nx][ny]=1;
                        q.push({nx,ny});
                    }
                }
            }
        }
    }
    void solve(vector<vector<char>>& board) {
        int n = board.size();
        int m = board[0].size();
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(int i=0;i<n;i++){
            if(board[i][0]=='O'){
                bfs1(board,vis,i,0);
            }
            if(board[i][m-1]=='O'){
                bfs1(board,vis,i,m-1);
            }
        }

        for(int i=1;i<m-1;i++){
            if(board[0][i]=='O'){
                bfs1(board,vis,0,i);
            }
            if(board[n-1][i]=='O'){
                bfs1(board,vis,n-1,i);
            }
        }

        for(int i=1;i<n-1;i++){
            for(int j=1;j<m-1;j++){
                if(board[i][j]=='O' && !vis[i][j]){
                    board[i][j] = 'X';
                }
            }
        }
       
    }
};
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