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