<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 dfs(int i, int j, vector<vector<char>>& board, vector<vector<int>>& vis, bool &flag){
        int n = board.size();
        int m = board[0].size();
        if(i==0 || i==n-1 || j==0 || j==m-1){
            flag = false;
        }
        vis[i][j] =1;
        int a[]= {0, 0, -1, 1};
        int b[] = {1, -1, 0, 0};
        for(int k=0; k<4; k++){
            int x = a[k]+i;
            int y = b[k]+j;
            if(x>=0 && x<n && y>=0 &&y<m && vis[x][y] != 1 && board[x][y] == 'O'){
                dfs(x, y, board, vis, flag);
            }
        }
        return flag;
    }
    void markdfs(int i, int j, vector<vector<char>>& board){
        int n = board.size();
        int m = board[0].size();
        int a[]= {0, 0, -1, 1};
        int b[] = {1, -1, 0, 0};
        board[i][j] = 'X';
        for(int k=0; k<4; k++){
            int x = a[k]+i;
            int y = b[k]+j;
            if(x>=0 && x<n && y>=0 &&y<m && board[x][y] != 'X'){
                markdfs(x, y, board);
            }
        }
    }
    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++){
            for(int j=0; j<m; j++){
                bool flag = true;
                if(board[i][j] == 'O' && vis[i][j] == 0){
                    if(dfs(i, j, board, vis, flag)){
                        cout<<"hi";
                        markdfs(i, j, board);
                    }
                }
            }
        }
    }
};
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