adventofcode/2018/day05/problem

Advent of Code

--- Day 5: Alchemical Reduction ---

   You've managed to sneak in to the prototype suit manufacturing lab. The
   Elves are making decent progress, but are still struggling with the suit's
   size reduction capabilities.

   While the very latest in 1518 alchemical technology might have solved their
   problem eventually, you can do better. You scan the chemical composition of
   the suit's material and discover that it is formed by extremely long
   polymers (one of which is available as your puzzle input).

   The polymer is formed by smaller units which, when triggered, react with
   each other such that two adjacent units of the same type and opposite
   polarity are destroyed. Units' types are represented by letters; units'
   polarity is represented by capitalization. For instance, r and R are units
   with the same type but opposite polarity, whereas r and s are entirely
   different types and do not react.

   For example:

     • In aA, a and A react, leaving nothing behind. • In abBA, bB destroys
     itself, leaving aA. As above, this then destroys itself, leaving nothing.
     • In abAB, no two adjacent units are of the same type, and so nothing
     happens. • In aabAAB, even though aa and AA are of the same type, their
     polarities match, and so nothing happens.

   Now, consider a larger example, dabAcCaCBAcCcaDA:

 dabAcCaCBAcCcaDA  The first 'cC' is removed.
 dabAaCBAcCcaDA    This creates 'Aa', which is removed.
 dabCBAcCcaDA      Either 'cC' or 'Cc' are removed (the result is the same).
 dabCBAcaDA        No further actions can be taken.

   After all possible reactions, the resulting polymer contains 10 units.

   How many units remain after fully reacting the polymer you scanned? (Note:
   in this puzzle and others, the input is large; if you copy/paste your input,
   make sure you get the whole thing.)

   Your puzzle answer was 10878.

--- Part Two ---

   Time to improve the polymer.

   One of the unit types is causing problems; it's preventing the polymer from
   collapsing as much as it should. Your goal is to figure out which unit type
   is causing the most problems, remove all instances of it (regardless of
   polarity), fully react the remaining polymer, and measure its length.

   For example, again using the polymer dabAcCaCBAcCcaDA from above:

     • Removing all A/a units produces dbcCCBcCcD. Fully reacting this polymer
     produces dbCBcD, which has length 6.
     • Removing all B/b units produces daAcCaCAcCcaDA. Fully reacting this
     polymer produces daCAcaDA, which has length 8.
     • Removing all C/c units produces dabAaBAaDA. Fully reacting this polymer
     produces daDA, which has length 4.
     • Removing all D/d units produces abAcCaCBAcCcaA. Fully reacting this
     polymer produces abCBAc, which has length 6.

   In this example, removing all C/c units was best, producing the answer 4.

   What is the length of the shortest polymer you can produce by removing all
   units of exactly one type and fully reacting the result?

   Your puzzle answer was 6874.

   Both parts of this puzzle are complete! They provide two gold stars: **

References

   Visible links
   . https://adventofcode.com/
   . https://adventofcode.com/2018/about
   . https://adventofcode.com/2018/events
   . https://adventofcode.com/2018/settings
   . https://adventofcode.com/2018/auth/logout
   . Advent of Code Supporter
	https://adventofcode.com/2018/support
   . https://adventofcode.com/2018
   . https://adventofcode.com/2018
   . https://adventofcode.com/2018/support
   . https://adventofcode.com/2018/sponsors
   . https://adventofcode.com/2018/leaderboard
   . https://adventofcode.com/2018/stats
   . https://adventofcode.com/2018/sponsors
   . https://en.wikipedia.org/wiki/Polymer
   . https://adventofcode.com/2018
   . https://adventofcode.com/2018/day/5/input