<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 dfs(int x , int y, vector<vector<int>>& visited ,vector<vector<char>>& board){
        if (x >= board.size() || y >= board[0].size() || x< 0 || y<0 || visited[x][y] == 1) return;

        if (board[x][y] == 'X') return;


        visited[x][y] = 1;
        

        vector<vector<int>> dirs = {{1,0},{0,1},{-1,0},{0,-1}};

        for (int i = 0 ; i < 4 ; i++){
            dfs(x+dirs[i][0],y+dirs[i][1],visited,board);
        }
    }
    void solve(vector<vector<char>>& board) {
        int m = board.size();
        int n = board[0].size();
        vector<pair<int,int>> zeroes;
        // zeroes on the edges

        for (int i = 0 ; i < m ; i++){
            if (board[i][0] == 'O') zeroes.push_back({i,0});
        }
        for (int i = 0 ; i < m ; i++){
            if (board[i][n-1] == 'O') zeroes.push_back({i,n-1});
        }
        for (int j = 0 ; j < n ; j++){
            if (board[0][j] == 'O') zeroes.push_back({0,j});
        }
        for (int j = 0 ; j < n ; j++){
            if (board[m-1][j] == 'O') zeroes.push_back({m-1,j});
        }
        vector<vector<int>> visited (m,vector<int>(n,0));
        for (auto i : zeroes){
            int x = i.first;
            int y = i.second;
            if (visited[x][y] == 0){
                dfs(x,y,visited,board);
            }

        }

        for (int i = 0 ; i < m ; i++){
            for (int j = 0 ; j < n ; j++){
                if (visited[i][j] == 0 && board[i][j] == 'O'){
                    board[i][j] = 'X';
                }
            }
        }



    }
};
25906