Advent of Code

--- Day 11: Radioisotope Thermoelectric Generators ---

   You come upon a column of four floors that have been entirely sealed off
   from the rest of the building except for a small dedicated lobby. There are
   some radiation warnings and a big sign which reads "Radioisotope Testing
   Facility".

   According to the project status board, this facility is currently being used
   to experiment with Radioisotope Thermoelectric Generators (RTGs, or simply
   "generators") that are designed to be paired with specially-constructed
   microchips. Basically, an RTG is a highly radioactive rock that generates
   electricity through heat.

   The experimental RTGs have poor radiation containment, so they're
   dangerously radioactive. The chips are prototypes and don't have normal
   radiation shielding, but they do have the ability to generate an
   electromagnetic radiation shield when powered. Unfortunately, they can only
   be powered by their corresponding RTG. An RTG powering a microchip is still
   dangerous to other microchips.

   In other words, if a chip is ever left in the same area as another RTG, and
   it's not connected to its own RTG, the chip will be fried. Therefore, it is
   assumed that you will follow procedure and keep chips connected to their
   corresponding RTG when they're in the same room, and away from other RTGs
   otherwise.

   These microchips sound very interesting and useful to your current
   activities, and you'd like to try to retrieve them. The fourth floor of the
   facility has an assembling machine which can make a self-contained, shielded
   computer for you to take with you - that is, if you can bring it all of the
   RTGs and microchips.

   Within the radiation-shielded part of the facility (in which it's safe to
   have these pre-assembly RTGs), there is an elevator that can move between
   the four floors. Its capacity rating means it can carry at most yourself and
   two RTGs or microchips in any combination. (They're rigged to some heavy
   diagnostic equipment - the assembling machine will detach it for you.) As a
   security measure, the elevator will only function if it contains at least
   one RTG or microchip. The elevator always stops on each floor to recharge,
   and this takes long enough that the items within it and the items on that
   floor can irradiate each other. (You can prevent this if a Microchip and its
   Generator end up on the same floor in this way, as they can be connected
   while the elevator is recharging.)

   You make some notes of the locations of each component of interest (your
   puzzle input). Before you don a hazmat suit and start moving things around,
   you'd like to have an idea of what you need to do.

   When you enter the containment area, you and the elevator will start on the
   first floor.

   For example, suppose the isolated area has the following arrangement:

 The first floor contains a hydrogen-compatible microchip and a
 lithium-compatible microchip.

 The second floor contains a hydrogen generator.

 The third floor contains a lithium generator.

 The fourth floor contains nothing relevant.

   As a diagram (F# for a Floor number, E for Elevator, H for Hydrogen, L for
   Lithium, M for Microchip, and G for Generator), the initial state looks like
   this:

 F4 .  .  .  .  .
 F3 .  .  .  LG .
 F2 .  HG .  .  .
 F1 E  .  HM .  LM

   Then, to get everything up to the assembling machine on the fourth floor,
   the following steps could be taken:

     • Bring the Hydrogen-compatible Microchip to the second floor, which is
       safe because it can get power from the Hydrogen Generator:

 F4 .  .  .  .  .
 F3 .  .  .  LG .
 F2 E  HG HM .  .
 F1 .  .  .  .  LM

     • Bring both Hydrogen-related items to the third floor, which is safe
       because the Hydrogen-compatible microchip is getting power from its
       generator:

 F4 .  .  .  .  .
 F3 E  HG HM LG .
 F2 .  .  .  .  .
 F1 .  .  .  .  LM

     • Leave the Hydrogen Generator on floor three, but bring the
       Hydrogen-compatible Microchip back down with you so you can still use the
       elevator:

 F4 .  .  .  .  .
 F3 .  HG .  LG .
 F2 E  .  HM .  .
 F1 .  .  .  .  LM

     • At the first floor, grab the Lithium-compatible Microchip, which is safe
       because Microchips don't affect each other:

 F4 .  .  .  .  .
 F3 .  HG .  LG .
 F2 .  .  .  .  .
 F1 E  .  HM .  LM

     • Bring both Microchips up one floor, where there is nothing to fry them:

 F4 .  .  .  .  .
 F3 .  HG .  LG .
 F2 E  .  HM .  LM
 F1 .  .  .  .  .

     • Bring both Microchips up again to floor three, where they can be
       temporarily connected to their corresponding generators while the elevator
       recharges, preventing either of them from being fried:

 F4 .  .  .  .  .
 F3 E  HG HM LG LM
 F2 .  .  .  .  .
 F1 .  .  .  .  .

     • Bring both Microchips to the fourth floor:

 F4 E  .  HM .  LM
 F3 .  HG .  LG .
 F2 .  .  .  .  .
 F1 .  .  .  .  .

     • Leave the Lithium-compatible microchip on the fourth floor, but bring
       the Hydrogen-compatible one so you can still use the elevator; this is
       safe because although the Lithium Generator is on the destination floor,
       you can connect Hydrogen-compatible microchip to the Hydrogen Generator
       there:

 F4 .  .  .  .  LM
 F3 E  HG HM LG .
 F2 .  .  .  .  .
 F1 .  .  .  .  .

     • Bring both Generators up to the fourth floor, which is safe because you
       can connect the Lithium-compatible Microchip to the Lithium Generator upon
       arrival:

 F4 E  HG .  LG LM
 F3 .  .  HM .  .
 F2 .  .  .  .  .
 F1 .  .  .  .  .

     • Bring the Lithium Microchip with you to the third floor so you can use
       the elevator:

 F4 .  HG .  LG .
 F3 E  .  HM .  LM
 F2 .  .  .  .  .
 F1 .  .  .  .  .

     • Bring both Microchips to the fourth floor:

 F4 E  HG HM LG LM
 F3 .  .  .  .  .
 F2 .  .  .  .  .
 F1 .  .  .  .  .

   In this arrangement, it takes 11 steps to collect all of the objects at the
   fourth floor for assembly. (Each elevator stop counts as one step, even if
   nothing is added to or removed from it.)

   In your situation, what is the minimum number of steps required to bring all
   of the objects to the fourth floor?

   Your puzzle answer was 31.

--- Part Two ---

   You step into the cleanroom separating the lobby from the isolated area and
   put on the hazmat suit.

   Upon entering the isolated containment area, however, you notice some extra
   parts on the first floor that weren't listed on the record outside:

     • An elerium generator.
     • An elerium-compatible microchip.
     • A dilithium generator.
     • A dilithium-compatible microchip.

   These work just like the other generators and microchips. You'll have to get
   them up to assembly as well.

   What is the minimum number of steps required to bring all of the objects,
   including these four new ones, to the fourth floor?

   Your puzzle answer was 55.

   Both parts of this puzzle are complete! They provide two gold stars: **

   At this point, all that is left is for you to admire your advent calendar.

   If you still want to see it, you can get your puzzle input.

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