<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 bfs(vector<vector<char>>& board,int i, int j,vector<vector<int>> &vis){
        int m = board.size();
        int n = board[0].size();
        queue<pair<int,int>> q;
        vector<pair<int,int>> v;
        q.push({i,j}); 
        vis[i][j] = 1;
        int dx[4] = {0,0,-1,1};
        int dy[4] = {-1,1,0,0};
        bool region = true;
        while(!q.empty()){
            auto p = q.front();
            q.pop();
            v.push_back({p.first,p.second});
            for(int i = 0; i<4; i++){
                int nx = p.first + dx[i];
                int ny = p.second + dy[i];
                if((nx < 0 || ny < 0 || nx >= m || ny >= n)){
                    continue;
                }
                if((nx == 0 || ny == 0 || nx == m-1 || ny == n-1) && board[nx][ny] == 'O'){
                    region = false;
                }
                if(board[nx][ny] == 'O' && !vis[nx][ny]){
                    vis[nx][ny] = 1;
                    q.push({nx,ny});
                }
            }
        }
        if(!region){
            return;
        }
        for(int k = 0; k<v.size(); k++){
            board[v[k].first][v[k].second] = 'X';
        }
    }
    void solve(vector<vector<char>>& board) {
        int m = board.size();
        int n = board[0].size();
        vector<vector<int>> vis(m,vector<int>(n,0));
        for(int i = 1; i<m-1; i++){
            for(int j = 1; j<n-1; j++){
                if(board[i][j] == 'O' && vis[i][j] == 0){
                    bfs(board,i,j,vis);
                }
            }
        }
    }
};
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