<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 isSafe(int r , int c , int m , int n)
    {
        return (r >=0 && r < m && c >=0 && c< n); 
    }
    void floodFill(int r , int c , int m , int n ,  vector<vector<char>>&board)
    {
        board[r][c] = 'V';

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

        for(int k = 0 ; k < 4 ; k++)
        {
            int newr = r + dirs[k][0];
            int newc = c + dirs[k][1];
            if(isSafe(newr , newc , m , n) && board[newr][newc] == 'O')
                floodFill(newr,newc,m,n,board); 
        }
    }
// Corrected solve() function:
void solve(vector<vector<char>>& board) {
    int m = board.size();
    if (m == 0) return;  // Handle empty board
    int n = board[0].size();

    // Step 1 - go over the boundary and connected regions and mark as visited
    for (int i = 0; i < n; i++) {
        if (board[0][i] == 'O') floodFill(0, i, m, n, board);
        if (board[m-1][i] == 'O') floodFill(m-1, i, m, n, board);
    }
    
    for (int j = 0; j < m; j++) {
        if (board[j][0] == 'O') floodFill(j, 0, m, n, board);
        if (board[j][n-1] == 'O') floodFill(j, n-1, m, n, board);
    }
    
    // Mark remaining 'O's with 'X' and restore 'V's to 'O'
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++) {
            if (board[i][j] == 'O')
                board[i][j] = 'X';
            else if (board[i][j] == 'V')
                board[i][j] = 'O';
        }
    }
}
};
19006