<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:
    int rows, cols;
    vector<vector<bool>> visited;
    vector<pair<int, int>> directions = {{0, 1}, {0, -1}, {-1, 0}, {1, 0}};
    void bfs(int r, int c, vector<vector<char>>& board) {
        vector<pair<int, int>> coords;
        queue<pair<int, int>> q;
        q.push({r, c});
        coords.push_back({r, c});
        visited[r][c] = true;

        bool surrounded = true;

        while (!q.empty()) {
            r = q.front().first;
            c = q.front().second;
            q.pop();

            if (r == 0 || c == 0 || r == rows - 1 || c == cols - 1) surrounded = false;

            for (const pair<int, int>& d : directions) {
                int dr = r + d.first, dc = c + d.second;
                if (dr >= 0 && dr < rows && dc >= 0 && dc < cols && !visited[dr][dc] && board[dr][dc] == 'O') {
                    q.push({dr, dc});
                    coords.push_back({dr, dc});
                    visited[dr][dc] = true;
                }
            }
        }

        if (surrounded) {
            for (const pair<int, int>& c : coords) {
                board[c.first][c.second] = 'X';
            }
        }
    }
    void solve(vector<vector<char>>& board) {
        ios_base::sync_with_stdio(false);
        cin.tie(nullptr);
        cout.tie(nullptr);

        rows = board.size();
        cols = board[0].size();
        visited = vector<vector<bool>>(rows, vector<bool>(cols, false));

        for (int r = 0; r < rows; r++) {
            for (int c = 0; c < cols; c++) {
                if (board[r][c] == 'O' && !visited[r][c]) {
                    bfs(r, c, board);
                }
            }
        }
    }
};
16246