<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:
unordered_map<int,vector<int>>u;
vector<int>t,l,vis;
int timer=1;
vector<vector<int>>v;
void helper(int node,int par)
{
   t[node]=timer;
   l[node]=timer;
   timer++;
   vis[node]=1;

   for(auto &nb:u[node])
   {
    if(nb==par)
    continue;
      if(vis[nb]==0)
      {
        helper(nb,node);
        l[node]=min(l[node],l[nb]);
        if(t[node]<l[nb])
        {
            v.push_back({node,nb});
        }
      }
      else
      {
          l[node]=min(l[node],l[nb]);
      }


   }
}
    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& connections) {
        // remove that edge which will increase the number of connected component

        // all edge that is part of cycle will not be included in the answer
      for(auto i:connections)
      {
        u[i[0]].push_back(i[1]);
        u[i[1]].push_back(i[0]);
      }
      t.resize(n,0);
      vis.resize(n,0);
      l.resize(n,INT_MAX);

      helper(0,-1);
      return v;

      
    }
};
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