<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 vis[201][201];
    void reset(){
        for(int i = 0; i < 201; i++){
            for(int j = 0; j < 201; j++) vis[i][j] = 0;
        }
    }
    vector<pair<int, int>> movements = {
        {0, 1}, {1, 0}, {-1, 0}, {0, -1}
    };
    bool valid(int r, int c, int n, int m){
        return r >= 0 && c >= 0 && r < n && c < m;
    }
    void remove(vector<vector<char>>& board, int row, int col){
        board[row][col] = 'X';
        // vis[row][col] = 1;
        int n = board.size();
        int m = board[0].size();
        for(auto &moves: movements){
            int newr = row+moves.first;
            int newc = col+moves.second;
            if(!valid(newr, newc, n, m)) continue;
            // if(vis[newr][newc]) continue;
            if(board[newr][newc] == 'X') continue;
            remove(board, newr, newc);
        }
    }
    bool check(vector<vector<char>>& board, int row, int col){
        vis[row][col] = 1;
        bool ans = false;
        int n = board.size();
        int m = board[0].size();
        for(auto &moves: movements){
            int newr = row+moves.first;
            int newc = col+moves.second;
            if(!valid(newr, newc, n, m)) return true;
            if(vis[newr][newc]) continue;
            if(board[newr][newc] == 'X') continue;
            ans |= check(board, newr, newc);
        }
        return ans;
    }
    void solve(vector<vector<char>>& board) {
        int n = board.size();
        int m = board[0].size();
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(board[i][j] == 'O'){
                    reset();
                    if(!check(board, i, j)){
                        // reset();
                        remove(board, i, j);
                    }
                }
            }
        }
    }
};
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