102 lines
3.4 KiB
Plaintext
102 lines
3.4 KiB
Plaintext
Advent of Code
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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
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brightly, and he needs medicine.
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Red-Nosed Reindeer biology isn't similar to regular reindeer biology;
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Rudolph is going to need custom-made medicine. Unfortunately, Red-Nosed
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Reindeer chemistry isn't similar to regular reindeer chemistry, either.
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The North Pole is equipped with a Red-Nosed Reindeer nuclear fusion/fission
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plant, capable of constructing any Red-Nosed Reindeer molecule you need. It
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works by starting with some input molecule and then doing a series of
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replacements, one per step, until it has the right molecule.
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However, the machine has to be calibrated before it can be used. Calibration
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involves determining the number of molecules that can be generated in one
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step from a given starting point.
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For example, imagine a simpler machine that supports only the following
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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
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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
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HOOH appears twice) after one replacement from HOH. Santa's favorite
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molecule, HOHOHO, can become 7 distinct molecules (over nine replacements:
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six from H, and three from O).
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The machine replaces without regard for the surrounding characters. For
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example, given the 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
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bottom, the medicine molecule for which you need to calibrate the machine.
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How many distinct molecules can be created after all the different ways you
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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
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fabrication.
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Molecule fabrication always begins with just a single electron, e, and
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applying replacements 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
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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
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be made in 6 steps.
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How long will it take to make the medicine? Given the available replacements
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and the medicine molecule in your puzzle input, what is the fewest number of
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steps to go from e to the medicine 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
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puzzle.
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If you still want to see it, you can get your puzzle input.
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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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