There are n servers numbered from 0 to n-1
connected by undirected server-to-server connections forming a network
where connections[i] = [a, b] represents a connection between servers
a and b. Any server can reach any other server directly or
indirectly through the network.
A critical connection is a connection that, if removed, will make some server unable to reach some other server.
Return all critical connections in the network in any order.
Example 1:

Input: n = 4, connections = [[0,1],[1,2],[2,0],[1,3]] Output: [[1,3]] Explanation: [[3,1]] is also accepted.
Constraints:
1 <= n <= 10^5n-1 <= connections.length <= 10^5connections[i][0] != connections[i][1]