There are `n` servers numbered from `0` to `n - 1` connected by undirected server-to-server `connections` forming a network where `connections[i] = [ai, bi]` represents a connection between servers `ai` and `bi`. Any server can reach other servers directly or indirectly through the network.

A critical connection is a connection that, if removed, will make some servers 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.

Example 2:

    Input: n = 2, connections = [[0,1]]
    Output: [[0,1]]

Constraints:

- `2 <= n <= 105`
- `n - 1 <= connections.length <= 105`
- `0 <= ai, bi <= n - 1`
- `ai != bi`
- There are no repeated connections.