Google Interview Problem #9 — Interval Active Users Table – interview proxy – VO prep

You are given a list of users, each with a start time and an end time.
For each time interval where the set of active users changes, output:

• the interval start
• the interval end
• the list of users active during that interval

Input Example

Name   | Start | End
-------|-------|-----
Abby   | 10    | 100
Ben    | 50    | 70
Carla  | 60    | 120
David  | 150   | 300

Output Example

Start | End | Names
------|-----|-------------------------
10    | 50  | Abby
50    | 60  | Abby, Ben
60    | 70  | Abby, Ben, Carla
70    | 100 | Abby, Carla
100   | 120 | Carla
150   | 300 | David

Convert all start/end into events:

• (time, +user) for start
• (time, -user) for end

Sort events and sweep from left to right.
Maintain an active user set:

• Add user on start event
• Remove user on end event

Between consecutive event times, output a time interval with the current active users.

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