<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:
    map<pair<int,int>,int>m;
    vector<int>rank;
    vector<vector<int>>gr;
    int dfs(int src,int par, int dep, int n)
    {
        if(rank[src]>=0)
        {
            return rank[src];
        }
        rank[src]=dep;
        int ans=n;
        for(auto i:gr[src])
        {
            if(i!=par)
            {
                int a=dfs(i,src,dep+1,n);
                if(a<=dep)
                {
                    m[{src,i}]++;
                    m[{i,src}]++;
                }
                ans=min(a,ans);
            }
        }
        return ans;
    }
    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& con) {
        rank.resize(n,-2);
        gr.resize(n+1);
        for(int i=0;i<con.size();++i)
        {
            gr[con[i][0]].push_back(con[i][1]);
            gr[con[i][1]].push_back(con[i][0]);
        }
        int a=dfs(0,0,0,n);
        vector<vector<int>>ans;
        for(int i=0;i<con.size();++i)
        {
            if(m[{con[i][0],con[i][1]}]==0)
            {
                ans.push_back({con[i][0],con[i][1]});
            }
        }
        return ans;

    }
};
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