Find earliest time all riders become connected

You are given activity logs for a ride-sharing app. Each log entry indicates that two riders shared a ride at a certain time, which creates an undirected connection between them (they can “reach” each other either directly or through other riders).

Problem

Given:

• An integer n = number of riders, labeled 0..n-1 .
• A list logs , where each entry is [timestamp, a, b] meaning rider a and rider b shared a ride at timestamp .

Return the earliest timestamp at which all riders become mutually connected (i.e., the graph of riders becomes a single connected component). If this never happens, return -1.

Notes / Constraints

• logs may be unsorted.
• Multiple logs can share the same timestamp.
• You may assume 0 <= a, b < n , a != b .
• Choose reasonable time and space complexity for large inputs (e.g., up to 1e5 logs).

Follow-up (harder variant)

Now suppose riders can also block each other. A block means two riders should be treated as not connected, even if there is a path between them that would otherwise connect them.

You may model this as additional events like [timestamp, "BLOCK", x, y] (and optionally [timestamp, "UNBLOCK", x, y]).

Discuss how you would modify your approach to support block events, and how you would determine the earliest time when all riders are mutually connected under these constraints.