<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, int parent,vector<int> adj[],vector<int>& disc,vector<int> &low,vector<bool> &visited,vector<vector<int>> &bridges,int &count){
    disc[node]=low[node]=count;
    visited[node]=1;

    for(int j=0;j<adj[node].size();j++){
        int neigh=adj[node][j];

        if(neigh==parent){
            continue;
        }
        else if(visited[neigh]==1){
            low[node]=min(low[node],low[neigh]);
        }
        else{
            count++;
            DFS(neigh,node,adj,disc,low,visited,bridges,count);

            //Bridge Check
            if(low[neigh]>disc[node]){
                vector<int> temp={node,neigh};
                bridges.push_back(temp);
            }

            low[node]=min(low[node],low[neigh]);
        }
    }
}
    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& connections) {
        
        //Create adjacency List
        vector<int> adj[n];

        for(int i=0;i<connections.size();i++){
            int u=connections[i][0];
            int v=connections[i][1];

            adj[u].push_back(v);
            adj[v].push_back(u);
        }

        //Answer vector
        vector<vector<int>> bridges;

        //Two vectors for storing discovery number and low
        vector<int> disc(n);
        vector<int> low(n);

        vector<bool> visited(n,0);
        int count=0;

        DFS(0,-1,adj,disc,low,visited,bridges,count);

        return bridges;
    }
};
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