<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:


    vector<vector<int>> vis1,vis2;
    vector<vector<char>> arr;
    int n,m;

    bool check(int x,int y){
        if(min(x,y)<0 || x>=n || y>=m)
            return false;
        return true;
    }

    int dx[4]={1,0,-1,0};
    int dy[4]={0,-1,0,1};

    void capture(int x,int y){
        int xx,yy;
        // cout<<x<<" "<<y<<endl;
        arr[x][y]='X';
        for(int i=0;i<4;i++){
            xx=dx[i]+x;
            yy=dy[i]+y;
            if(check(xx,yy) && arr[xx][yy]=='O'){
                arr[xx][yy]='X';
                capture(xx,yy);
            }
        }
    }

    bool dfs(int x,int y){
        if(x==n-1 || y==m-1 || min(x,y)==0)
            return false;
        if(vis1[x][y])
            return true;
        bool flag=true;
        int xx,yy;
        vis1[x][y]=1;
        for(int i=0;i<4;i++){
            xx=dx[i]+x;
            yy=dy[i]+y;
            if(check(xx,yy) && arr[xx][yy]=='O'){
                flag&=dfs(xx,yy);
            }
        }
        // cout<<x<<" "<<y<<" "<<flag<<endl;
        return flag;
    }

    void solve(vector<vector<char>>& board) {
        arr=board;
        n=arr.size();
        m=arr[0].size();
        vis1.resize(n,vector<int>(m,0));
        vis2.resize(n,vector<int>(m,0));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(!vis1[i][j] && arr[i][j]=='O' && dfs(i,j)){
                    capture(i,j);
                }
            }
        }
        board=arr;
    }
};
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