This year ended with a text adventure game that runs on our intcode VMs! To finish the game, you must collect the right set of items and pass through the security checkpoint. It was fun, creative, and a great way to end the event.
To solve the game on the night of, I hooked up some basic I/O to my intcode VM
and played the game manually. I went back and later added an autosolver, which
uses DFS with save states to build a graph of the game map while noting the
location of all items. It then uses networkx to navigate throughout the
maze, picking up all items. (Why networkx? The basic info collected during
the initial DFS is only sufficient to plan paths starting from the root node.)
With all items, it heads to the security checkpoint and brute forces all combinations of items to see which are allowed to pass.
Potential room for improvement: Some items should not be picked up and make the game crash in creative ways. The VM could be programmed to save state and try picking up an item, then restore and blacklist the item if it didn't work. Instead, it uses a manually coded blacklist I created while playing the game manually.
Another point of improvement would be to make the brute force item search at the end a bit smarter. The game tells you if you're too heavy or too light, so any combinations of items that contain subsets of items that are too heavy on their own don't need to be tried.
2019 Day 25 on AdventOfCode.com
As you approach Santa's ship, your sensors report two important details:
First, that you might be too late: the internal temperature is -40 degrees.
Second, that one faint life signature is somewhere on the ship.
The airlock door is locked with a code; your best option is to send in a small droid to investigate the situation. You attach your ship to Santa's, break a small hole in the hull, and let the droid run in before you seal it up again. Before your ship starts freezing, you detach your ship and set it to automatically stay within range of Santa's ship.
This droid can follow basic instructions and report on its surroundings; you can communicate with it through an Intcode program (your puzzle input) running on an ASCII-capable computer.
As the droid moves through its environment, it will describe what it encounters. When it says Command?, you can give it a single instruction terminated with a newline (ASCII code 10). Possible instructions are:
- Movement via
north,south,east, orwest. - To take an item the droid sees in the environment, use the command
take <name of item>. For example, if the droid reports seeing ared ball, you can pick it up with takered ball. - To drop an item the droid is carrying, use the command
drop <name of item>. For example, if the droid is carrying agreen ball, you can drop it withdrop green ball. - To get a list of all of the items the droid is currently carrying, use the
command
inv(for "inventory").
Extra spaces or other characters aren't allowed - instructions must be provided precisely.
Santa's ship is a Reindeer-class starship; these ships use pressure-sensitive floors to determine the identity of droids and crew members. The standard configuration for these starships is for all droids to weigh exactly the same amount to make them easier to detect. If you need to get past such a sensor, you might be able to reach the correct weight by carrying items from the environment.
Look around the ship and see if you can find the password for the main airlock.
As you move through the main airlock, the air inside the ship is already heating up to reasonable levels. Santa explains that he didn't notice you coming because he was just taking a quick nap. The ship wasn't frozen; he just had the thermostat set to "North Pole".
You make your way over to the navigation console. It beeps. "Status: Stranded. Please supply measurements from 49 stars to recalibrate."
"49 stars? But the Elves told me you needed fifty--"
Santa just smiles and nods his head toward the window. There, in the distance, you can see the center of the Solar System: the Sun!
The navigation console beeps again.