<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>> dir = {{0,1},{1,0},{0,-1},{-1,0}};
    void solve(vector<vector<char>>& board) {
        int n = board.size();
        int m = board[0].size();
        vector<vector<bool>> vis(n,vector<bool>(m,false));
        for(int i=0;i<n;i++) {
            for(int j=0;j<m;j++) {
                if((i==0 || j==0 || i==n-1 || j==m-1) && board[i][j] == 'O') {
                    dfs(board,vis,i,j);
                }
            }
        }

        for(int i=0;i<n;i++) {
            for(int j=0;j<m;j++) {
                if(board[i][j] == 'A') {
                    board[i][j] = 'O';
                } else {
                    board[i][j] = 'X';
                }
            }
        }
        
    }
    bool dfs(vector<vector<char>> &board,vector<vector<bool>> &vis,int i,int j) {
        if(i<0 || j<0 || i>=board.size() || j>=board[0].size() || board[i][j] == 'X' || vis[i][j])
            return false;
        //cout << i << " " << j << endl;
        vis[i][j] = true;
        if(board[i][j]=='O')
            board[i][j]='A';
        bool left = dfs(board,vis,i,j-1);
        bool top = dfs(board,vis,i-1,j);
        bool right = dfs(board,vis,i,j+1);
        bool down = dfs(board,vis,i+1,j);
        //vis[i][j] = false;
        // if((left || right || top || down) && board[i][j] == 'X') {
        //     board[i][j] = 'A';
        // }
        // if((!left && !right && !top && !down) && board[i][j] == 'O') {
        //     board[i][j] = 'X';
        // }
        return left || right || top || down;
    }
};
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