Critical Connections in a Network

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 <= 10^5` `n-1 <= connections.length <= 10^5` `connections[i][0] != connections[i][1]` There are no repeated connections.