Find earliest time all riders become connected

You are given a time-ordered log of events involving Uber riders. Each event has a timestamp and two rider names.

Event types:

1. t X shared-ride-with Y — riders X and Y shared a ride at time t, which creates an (undirected) connection between them.

Two riders are considered connected if there is a path of shared rides between them (transitive connectivity). For example, if A shared with B and B shared with C, then A is connected to C.

Example (already sorted by time):

• t1 Alice shared-ride-with Bob
• t2 Charlie shared-ride-with Dan
• t3 Bob shared-ride-with Charlie
• t4 Alice shared-ride-with Eve
• t5 Bob shared-ride-with Dan

Task:

• Return the earliest timestamp at which all riders that appear in the logs become connected in a single connected component. If this never happens, return an appropriate value (e.g., -1).

Follow-up: The log may also contain block events:

• t X blocked Y — starting at time t, treat riders X and Y as no longer directly connected by their shared-ride relationship (i.e., the edge between X and Y is removed for times >= t, even if they shared earlier).

How would you modify your approach to still find the earliest time when all riders are connected, given that connections can be both added (shared-ride-with) and removed (blocked)?