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`)?