Advent of Code, day 13

day13.rb

#!/usr/bin/env ruby

# http://adventofcode.com/day/13

INPUT_PATTERN = /^(\w+) would (gain|lose) (\d+) happiness units by sitting next to (\w+).$/

@deltas = Hash[
  File.read("input").lines.map do |line|
    raise line.inspect unless line =~ INPUT_PATTERN
    person, sign, delta, neighbor = $~.captures
    delta = Integer(delta)
    delta *= -1 if sign == "lose"
    [[person, neighbor], delta]
  end
]

def people
  @deltas.keys.flatten.uniq
end

def best_happiness_delta
  people.permutation.map do |arrangement|
    arrangement << arrangement.first
    [arrangement, arrangement.reverse].flat_map do |a|
      a.each_cons(2).map do |pair|
        @deltas.fetch(pair)
      end
    end.reduce(&:+)
  end.max
end

# part 1
puts best_happiness_delta

# part2
people.each do |person|
  pair = [person, "Me"]
  @deltas[pair] = 0
  @deltas[pair.reverse] = 0
end
puts best_happiness_delta