<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:
 int timer=0;
void dfs(int node,vector<int>&visit,vector<int>adj[],vector<vector<int>>&ans,vector<int>&parent,vector<int>&low,vector<int>&tin){
    visit[node]=1;
    timer++;
    low[node]=tin[node]=timer;
      for(auto adjNode:adj[node]){
             if(!visit[adjNode]){
                parent[adjNode]=node;
        dfs(adjNode,visit,adj,ans,parent,low,tin);
        low[node]=min(low[node],low[adjNode]);
        if(low[adjNode]>tin[node]){
            ans.push_back({node,adjNode});
        }
             }   
             else if(adjNode!=parent[node]){
                low[node]=min(low[node],low[adjNode]);
             }
      }
      return;
}
    vector<vector<int>> criticalConnections(int n, vector<vector<int>>&edges) {
        vector<int>adj[n];
        int i=0;
        while(i<edges.size()){
            int u=edges[i][0];
            int v=edges[i][1];
            adj[u].push_back(v);
            adj[v].push_back(u);
            i++;
        }
        vector<vector<int>>ans;
        vector<int>parent(n);
         i=0;
        while(i<n){
            parent[i]=i;
            i++;
        }
        vector<int>low(n);
        vector<int>tin(n);
        vector<int>visit(n,0);
        dfs(0,visit,adj,ans,parent,low,tin);
        return ans;
    }
};
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