BAPHL 11 / Solution - The Azran Vault

Solution - The Azran Vault (#011)

To solve this puzzle, teams needed to transmit a nine-letter English word via five three-letter English words, which would be scrambled in transmission. There are many ways to do this, and we didn't have a “correct” solution in mind, but successful teams often used one or more of the following observations to get their code across.

Your scheme doesn't always need to work. Teams had as many tries as they wanted (within reason), so they could just try with another word if their first transmission wasn't successful.

You don't need to transmit all the letters. On a related note, transmitting most of the letters will often suffice to reconstruct the codeword. It's even more likely to work if you transmit only the word's consonants.

Decompose the word. A lot of teams used the letters in their given word to build three-letter words which would clue the answer. Many nine-letter words are unique enough that they can often be completely determined from their letters alone.

Here are two simple example codes that we saw teams using:

Send only the odd letters of the word. Construct five three-letter words that, when alphabetized, spell out the odd letters of the word with their middle or last letters. For example, if the word was
```
UNDERSELL
```
then the odd letters would be
```
U D R E L
```
and teams might send
```
BUG EDS FRY PEA SLY
```
The receiver could alphabetize their words and read off the middle letters to get
```
U D R E L
```
Send (up to 5) consonants in the word. The way this works is similar to the scheme above.
Decompose the word into three three-letter words. In the case of
```
UNDERSELL
```
this could be done by transmitting
```
DEL ELS RUN
```
The remaining two words could be used to convey additional information (for instance, the first two letters of the given word) but some teams were able to reconstruct their word without doing this.

When teams successfully transmitted their 9-letter word, we gave them the answer, which was JOUST.

For curiosity's sake, here is the list of words we used at the hunt:

```
UNDERSELL
```
```
ACOUSTICS
```
```
PACIFYING
```
```
CARNELIAN
```
```
WEDNESDAY
```
```
CAFETERIA
```

Finally, a few teams asked about whether the words used in the puzzle had to be English. The puzzle is a little trickier when we require English words, but it turns out to still be interesting when we're allowed to send arbitrary strings!

In fact, this puzzle was inspired by a computer science contest problem called Parrots, which allows you to send any string you like with your parrots. On the flip side, that puzzle is harder in other ways (for instance, your scheme must work with 100% probability). Take a look if you're interested in the other interpretation!