<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:
vector<vector<int>> ans;
void DFS(int src, int parent, vector<int> adj[], vector<int> &low, vector<int> &disc)
{
    static int time = 0;
    disc[src] = low[src] = time;
    time++;
    for (auto &it : adj[src])
    {
        if (disc[it] == -1)
        {
            DFS(it, src, adj, low, disc);
            low[src] = min(low[src], low[it]);
           if(it!=parent and low[it]>disc[src])  ans.push_back({src,it});
        }
        else if ( it != parent)
        {
            low[src] = min(low[src], disc[it]);
        }
    }
  
}
vector<vector<int>> criticalConnections(int n, vector<vector<int>> &connections)
{
    vector<int> adj[n];
    for (auto &it : connections)
    {
        adj[it[0]].push_back(it[1]);
        adj[it[1]].push_back(it[0]);
    }
    vector<int> low(n, -1), disc(n, -1);


     DFS(0, -1, adj, low, disc);
    return ans;
}
};
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