Solutions for 2022, as well as 2015-2018 and 2019 up to day 11

2015/day19-medicine_for_rudolph/challenge.txt

@@ -0,0 +1,71 @@
+\--- 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 `535`.
+
+\--- 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 `212`.
+
+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](/2015).
+
+If you still want to see it, you can [get your puzzle input](19/input).