Internationali­zation Puzzles

Out of date

CERN. Right on the French-Swiss border. Discovery site of the Higgs Boson. Birthplace of the world wide web.

The IT department at CERN is responsible for software maintenance and data management for all their physics research programs. As a member of that IT department, you take care of one of the most advanced and complex international collaboration projects, namely the gravitational wave research program.

As in puzzle 2, you receive data from research stations worldwide. You have to combine this data, and look for a single moment where all detectors found a signal at exactly the same time.

Consider the following dataset, which serves as your test input:

2024-04-09 18:49:00; Africa/Casablanca
2024-04-10 02:19:00; Asia/Pyongyang
2024-04-10 04:49:00; Antarctica/Casey
2024-04-12 12:13:00; Asia/Pyongyang
2024-04-12 15:54:00; Africa/Casablanca
2024-04-12 16:43:00; Africa/Casablanca
2024-04-13 00:24:00; Asia/Pyongyang
2024-04-13 01:54:00; Antarctica/Casey
2024-04-13 07:43:00; Antarctica/Casey

These are local times, combined with an IANA time zone identifier for that research station. You convert all of these to UTC, and sort them:

2024-04-09T17:19:00+00:00; Asia/Pyongyang
2024-04-09T17:49:00+00:00; Antarctica/Casey
2024-04-09T18:49:00+00:00; Africa/Casablanca
2024-04-12T03:13:00+00:00; Asia/Pyongyang
2024-04-12T14:54:00+00:00; Antarctica/Casey
2024-04-12T15:24:00+00:00; Asia/Pyongyang
2024-04-12T15:54:00+00:00; Africa/Casablanca
2024-04-12T16:43:00+00:00; Africa/Casablanca
2024-04-12T20:43:00+00:00; Antarctica/Casey

Alas, no timestamp matches. Nothing has been discovered.

Over lunch at Restaurant 1, you discuss the lack of progress with a colleague from the IT department. "Don't give up, you're bound to find something eventually", she says. Then the topic changes to her project. Your colleague is heading a program to increase security of research labs around the world. "These academics don't give a rat's ass about IT security", she scoffs. "Just look at these eggheads in Casablanca. I just found out that they haven't updated their system since 2018."

"Really, not since 2018?", you say. Then you have an epiphany. "Sorry, gotta go!" You abandon your lunch and run back to your computer. If they haven't updated their software at all, they might still be running with an older version of the time zone database. You ought to re-do your analysis.

If you make some assumptions about which version of the time zone database was used by each research stations (and a given station used the same version throughout), you end up with the following result:

If we assume that:

Using these outdated UTC offsets, we find:

As you can see, there is actually a match! All three research stations reported a signal at exactly 2024-04-09T17:49:00+00:00.

The IT department at CERN is responsible for maintaining the software in all these research stations. This software includes a copy of the time zone database. Unfortunately, you couldn't find out which version was installed at each lab, so you'll have to guess. However, you do know which versions were released by your department. Checking the changelogs, you see that only the following versions of the time zone database were ever released: 2018c, 2018g, 2021b, 2023d. So the problem is limited to just those four versions. And fortunately, the history of time zones is well documented if you know where to look (see reading materials).

Assuming that each of the research stations is running on one of the four aforementioned versions, find the UTC timestamp where all research stations detected a signal. Your answer should be formatted as yyyy-mm-ddThh:mm:ss+00:00.

Reference & Reading materials

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