<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 {
private:
    void dfs(int row,int col,vector<vector<int>>& visited,
    vector<vector<char>>& board, bool switched){
        visited[row][col] = 1;

        if(switched) board[row][col] = 'X';

        int r[] = {0,0,-1,1};
        int c[] = {-1,1,0,0};

        int n = board.size();
        int m = board[0].size();

        for(int i = 0;i<4;i++){
            int nRow = row + r[i];
            int nCol = col + c[i];

            if(nRow>=0 && nRow<n && nCol>=0 && nCol<m
            && board[nRow][nCol] == 'O' && !visited[nRow][nCol]){
                dfs(nRow,nCol,visited,board,switched);
            }
        }
    }
public:
    void solve(vector<vector<char>>& board) {
        int n = board.size();
        int m = board[0].size();

        vector<vector<int>>visited(n,vector<int>(m,0));

        //safe gaurd border regions
        for(int j = 0;j<m;j++){
            if(board[0][j] == 'O' && !visited[0][j]){
                //cout<<"hello"<<endl;
                dfs(0,j,visited,board,false);
            }
        }
        for(int j = 0;j<m;j++){
            if(board[n-1][j] == 'O' && !visited[n-1][j]){
                dfs(n-1,j,visited,board,false);
            }
        }
        for(int i = 0;i<n;i++){
            if(board[i][0] == 'O' && !visited[i][0]){
                //cout<<"hello"<<endl;
                dfs(i,0,visited,board,false);
            }
        }
        for(int i = 0;i<n;i++){
            if(board[i][m-1] == 'O' && !visited[i][m-1]){
                //cout<<"hello"<<endl;
                dfs(i,m-1,visited,board,false);
            }
        }

        // bool canCapture = false;
        // for(int i = 0;i<n;i++){
        //     for(int j = 0;j<m;j++){
        //         if()
        //     }
        // }


        //capture other regions
        for(int i = 0;i<n;i++){
            for(int j = 0;j<m;j++){
                if(board[i][j] == 'O' && !visited[i][j]){
                    //cout<<"hello"<<endl;
                    dfs(i,j,visited,board,true);
                }
            }
        }
    }
};
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