Module day_22

This is my solution for Advent of Code - Day 22: Monkey Market

parse_input parses the inout file as a list of ints.

iterate_and_sum solves part 1, using pseudorandom_sequence to provide an iterator of the sequence from the seed by repeatedly calling NumberExtensions::next_secret.

bananas_from_best_diff_sequence solves part 2 by keeping track of the bananas earned by each leading sequence of four diffs, and then picking the maximum. For performance this packs the sequence into a 20-bit int using shift_diff_into_sequence_id to manage that.

Traits

• NumberExtensions 🔒

Functions

• bananas_from_best_diff_sequence 🔒
  Solves part 2, Build a map from price difference sequences to bananas bought, and pick the best.
• iterate_and_sum 🔒
  Solves part 1 - take the 2000th value from each seed’s pseudorandom sequence and sum
• parse_input 🔒
  The input file is one integer seed per line
• populate_sequence_scores 🔒
  This finds the price of banana each sequence of four diffs that are present in the sequence will fetch. These are added to a mutable Vec indexed by the sequence_id, which is the previous four diffs packed into an int by shift_diff_into_sequence_id. Once a diff has been seen for each seed, future instances of that sequence are ignored. Again this is managed using a Vec that keeps track of the last id that wrote to a specific sequence_id, which is allocated once and passed in for performance.
• pseudorandom_sequence 🔒
  Generate a pseudorandom iterator from a seed by repeatedly calling NumberExtensions::next_secret
• run
  The entry point for running the solutions with the ‘real’ puzzle input.
• shift_diff_into_sequence_id 🔒
  For performance reasons the sequence of four diffs before the current price is packed into a 20-bit integer