adventofcode/2015/day19/problem
2016-12-16 16:21:15 -06:00

108 lines
4.1 KiB
Plaintext
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

Advent of Code
br0xen 40*
• [About]
• [Stats]
• [Leaderboard]
• [Settings]
• [Log out]
--- Day 19: Medicine for Rudolph ---
Rudolph the Red-Nosed Reindeer is sick! His nose isn't shining very brightly, and he needs
medicine.
Red-Nosed Reindeer biology isn't similar to regular reindeer biology; Rudolph is going to need
custom-made medicine. Unfortunately, Red-Nosed Reindeer chemistry isn't similar to regular
reindeer chemistry, either.
The North Pole is equipped with a Red-Nosed Reindeer nuclear fusion/fission plant, capable of
constructing any Red-Nosed Reindeer molecule you need. It works by starting with some input
molecule and then doing a series of replacements, one per step, until it has the right
molecule.
However, the machine has to be calibrated before it can be used. Calibration involves
determining the number of molecules that can be generated in one step from a given starting
point.
For example, imagine a simpler machine that supports only the following replacements:
H => HO
H => OH
O => HH
Given the replacements above and starting with HOH, the following molecules could be generated:
 HOOH (via H => HO on the first H).
 HOHO (via H => HO on the second H).
 OHOH (via H => OH on the first H).
 HOOH (via H => OH on the second H).
 HHHH (via O => HH).
So, in the example above, there are 4 distinct molecules (not five, because HOOH appears twice)
after one replacement from HOH. Santa's favorite molecule, HOHOHO, can become 7 distinct
molecules (over nine replacements: six from H, and three from O).
The machine replaces without regard for the surrounding characters. For example, given the
string H2O, the transition H => OO would result in OO2O.
Your puzzle input describes all of the possible replacements and, at the bottom, the medicine
molecule for which you need to calibrate the machine. How many distinct molecules can be
created after all the different ways you can do one replacement on the medicine molecule?
Your puzzle answer was 518.
--- Part Two ---
Now that the machine is calibrated, you're ready to begin molecule fabrication.
Molecule fabrication always begins with just a single electron, e, and applying replacements
one at a time, just like the ones during calibration.
For example, suppose you have the following replacements:
e => H
e => O
H => HO
H => OH
O => HH
If you'd like to make HOH, you start with e, and then make the following replacements:
 e => O to get O
 O => HH to get HH
 H => OH (on the second H) to get HOH
So, you could make HOH after 3 steps. Santa's favorite molecule, HOHOHO, can be made in 6
steps.
How long will it take to make the medicine? Given the available replacements and the medicine
molecule in your puzzle input, what is the fewest number of steps to go from e to the medicine
molecule?
Your puzzle answer was 200.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should return to your advent calendar and try another puzzle.
If you still want to see it, you can get your puzzle input.
You can also [Shareon Twitter Google+ Reddit] this puzzle.
References
Visible links
. http://adventofcode.com/
. http://adventofcode.com/about
. http://adventofcode.com/stats
. http://adventofcode.com/leaderboard
. http://adventofcode.com/settings
. http://adventofcode.com/auth/logout
. http://adventofcode.com/
. http://adventofcode.com/day/19/input
. https://twitter.com/intent/tweet?text=I%27ve+completed+%22Medicine+for+Rudolph%22+%2D+Day+19+%2D+Advent+of+Code&url=http%3A%2F%2Fadventofcode%2Ecom%2Fday%2F19&related=ericwastl&hashtags=AdventOfCode
. https://plus.google.com/share?url=http%3A%2F%2Fadventofcode%2Ecom%2Fday%2F19
. http://www.reddit.com/submit?url=http%3A%2F%2Fadventofcode%2Ecom%2Fday%2F19&title=I%27ve+completed+%22Medicine+for+Rudolph%22+%2D+Day+19+%2D+Advent+of+Code