advent-of-code/2023/ruby/day_07.rb

HAND_STRENGTH = [
  [5],             # five of a kind
  [1, 4],          # four of a kind
  [2, 3],          # full house
  [1, 1, 3],       # three of a kind
  [1, 2, 2],       # two pair
  [1, 1, 1, 2],    # one pair
  [1, 1, 1, 1, 1], # high card
].reverse.each.with_index.to_h { [_1, _2] }

module PartOne
  CARD_STRENGTH = ((?2..?9).to_a + %w[ T J Q K A ]).each.with_index.to_h

  def self.strength(cards)
    tally = cards.tally
    strengths = [
      HAND_STRENGTH.fetch(tally.values.sort),
      *cards.map { CARD_STRENGTH.fetch(_1) },
    ]
    strengths.map { (?a.ord + _1).chr }.join
  end
end

module PartTwo
  CARD_STRENGTH = ([?J] + (?2..?9).to_a + %w[ T Q K A ]).each.with_index.to_h

  def self.strength(cards)
    tally = cards.tally
    jokers = tally.delete(?J) || 0
    counts = tally.values.sort
    if counts.empty?
      counts = [5]
    else
      counts[-1] += jokers
    end
    strengths = [
      HAND_STRENGTH.fetch(counts),
      *cards.map { CARD_STRENGTH.fetch(_1) },
    ]
    strengths.map { (?a.ord + _1).chr }.join
  end
end

hands = ARGF.read.scan(/(\w+)\s+(\d+)/).to_h { [_1.chars, _2.to_i ] }

p hands
  # .sort_by {|(hand,_)| PartOne::strength(hand) }
  .sort_by {|(hand,_)| PartTwo::strength(hand) }
  .map.with_index {|(_,bid),i| bid * (i+1) }
  .sum