<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 isValid(int n ,int m,int r,int c)
{
    if(r<0 || c <0 || r >n-1|| c>m-1 )
    {
        return false;
    }
    return true ; 
}
void dfs(int r,int c,vector<vector<char>>&board,vector<vector<int>>&vis,bool &toTake,vector<pair<int,int>>&temp)
{
    if(vis[r][c]==1)
    {
        return ;
    }
    temp.push_back({r,c});
    vis[r][c] = 1;
    int rd[4] = {1,-1,0,0};
    int cd[4] = {0,0,1,-1};
    if(r==0 || c == 0 || r == board.size()-1||c==board[0].size()-1)
    {
        toTake = false;
    }
    for(int i = 0 ; i<4;i++)
    {
        int row = r+rd[i];
        int col = c+cd[i];
        if(isValid(board.size(),board[0].size(),row,col)&&board[row][col]!='X')
        {
            dfs(row,col,board,vis,toTake,temp);
        }
    }
    
}
    void solve(vector<vector<char>>& board) {
        int n = board.size();
        int m = board[0].size();
        vector<pair<int,int>>pairs;
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(int i =0 ; i < n ; i++)
        {
            for(int j = 0 ; j < m ; j++)
            {
              bool toTake = true;
            vector<pair<int,int>>temp;
                if(vis[i][j]==0 && board[i][j]=='O')
                {
                    dfs(i,j,board,vis,toTake,temp);
                    if(toTake)
                    {
                        pairs.insert(pairs.end(),temp.begin(),temp.end());
                    }
                }
            }
        }
        for(auto it : pairs)
        {
            board[it.first][it.second] = 'X';
        }
       
    }
};
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