<p>There are <code>n</code> servers numbered from <code>0</code> to <code>n - 1</code> connected by undirected server-to-server <code>connections</code> forming a network where <code>connections[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> represents a connection between servers <code>a<sub>i</sub></code> and <code>b<sub>i</sub></code>. Any server can reach other servers directly or indirectly through the network.</p>

<p>A <em>critical connection</em> is a connection that, if removed, will make some servers unable to reach some other server.</p>

<p>Return all critical connections in the network in any order.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/09/03/1537_ex1_2.png" style="width: 198px; height: 248px;" />
<pre>
<strong>Input:</strong> n = 4, connections = [[0,1],[1,2],[2,0],[1,3]]
<strong>Output:</strong> [[1,3]]
<strong>Explanation:</strong> [[3,1]] is also accepted.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 2, connections = [[0,1]]
<strong>Output:</strong> [[0,1]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>n - 1 &lt;= connections.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub> &lt;= n - 1</code></li>
	<li><code>a<sub>i</sub> != b<sub>i</sub></code></li>
	<li>There are no repeated connections.</li>
</ul>

class Solution {
public:

    void dfs(int node,vector<int> &parent,vector<vector<int>> &adj,vector<int> &visit,int &count,vector<pair<int,int>> &data,int n,vector<vector<int>> &res){    

            visit[node] = 1;
            count++;
            data[node].first = count;
            int N = adj[node].size();
            for(int i=0;i<N;i++){
                int nbr = adj[node][i];
                if(visit[nbr]==0){
                    parent[nbr] = node;
                    dfs(nbr,parent,adj,visit,count,data,n,res);
                    data[node].second = min(data[node].second,data[nbr].second);
                    int start_time = data[node].first;
                    int furthest_pred = data[node].second;
                    int st = data[nbr].first;
                    int fp = data[nbr].second;
                    if (data[nbr].second > data[node].first) {
                        res.push_back({nbr,node});
                    }
                }
                else{
                    if(parent[node]!=nbr){
                        data[node].second = min(data[node].second,data[nbr].first);
                    }
                }
            }
            count++;
    }

    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& connections) {
            vector<vector<int>> adj(n);
            for(auto it:connections){
                int n1 = it[0];
                int n2 = it[1];

                adj[n1].push_back(n2);
                adj[n2].push_back(n1);
            }
            
            vector<pair<int,int>> data(n,{-1,INT_MAX});
            int count = -1;
            vector<int> visit(n,0);
            vector<int> parent(n,-1);
            vector<vector<int>> res;
            dfs(0,parent,adj,visit,count,data,n,res);
            // for(int i=0;i<n;i++){
            //     cout<<i<<" "<<data[i].first<<" "<<data[i].second<<endl;
            // }
           
            
            // for(int i=0;i<n;i++){
            //     int N = adj[i].size();
            //     int start_time = data[i].first;
            //     int furthest_pred = data[i].second;
            //     for(int j=0;j<N;j++){
            //         int nbr = adj[i][j];
            //         int st = data[nbr].first;
            //         int fp = data[nbr].second;
                   
            //         if (data[nbr].second > data[i].first) {
            //             vector<int> temp = {i, nbr};
            //             sort(temp.begin(), temp.end());
            //             s.insert(temp);
            //         }

            //     }
            // }
            // vector<vector<int>> res(s.begin(),s.end());
            return res;
    }
};
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