Ruby Solution to Poker Hands Dealer Problem: https://ruby-china.org/topics/30918

poker_hands.rb

PokerHand = Struct.new :player, :cards
class PokerHand
  Card = Struct.new :name, :value, :suit
  class Card
    def initialize name
      super name, '23456789TJQKA'.index(name[0]), name[1]
    end

    def <=> other
      value <=> other.value
    end

    def succ_value
      value == 12 ? 0 : value + 1
    end

    def desc
      %w[2 3 4 5 6 7 8 9 Ten Jack Queen King Ace][value]
    end
  end

  def initialize player, cards
    super player, cards.split.map {|c| Card.new c }.sort
  end

  def vs other
    %W[
      straight_flush
      four_of_a_kind
      full_house
      flush
      straight
      three_of_a_kind
      two_pairs
      pair
      high
    ].each do |m|
      value = send m
      other_value = other.send m
      if value or other_value
        value&.unshift m
        other_value&.unshift m
        announce_win *[(value || []), (other_value || [])].sort.reverse
        break
      end
    end
  end

  def announce_win win_cards, lose_cards
    win_cards.zip lose_cards do |c1, c2|
      if !c2
        puts "#{player} Wins. - with #{c1.gsub '_', ' '}"
        return
      end
      if (c1 <=> c2) == 1
        puts "#{player} Wins. - with high card: #{c1.desc}"
        return
      end
    end
    puts "Tie"
  end

  def straight_flush
    [cards.max] if flush and straight
  end

  def four_of_a_kind
    k = _largest_kind
    k.take 1 if k.size == 4
  end

  def full_house
    k1, k2 = _largest_kind 2
    [k1.first, k2.first] if k1.size == 3 and k2.size == 2
  end

  def flush
    high if cards.chunk(&:suit).count == 1
  end

  def straight
    high if cards.chunk_while{|c1, c2| c1.succ_value == c2.value}.count == 1
  end

  def three_of_a_kind
    k = _largest_kind
    k.take 1 if k.size == 3
  end

  def two_pairs
    k1, k2 = _largest_kind 2
    if k1.size == 2 and k2.size == 2
      pair_cards = [k1.first, k2.first]
      [pair_cards.max, pair_cards.min, *high]
    end
  end

  def pair
    k = _largest_kind
    [k.first, *high] if k.size == 2
  end

  def high
    cards.sort_by{|c| -c.value}
  end

  private def _largest_kind n=1
    cards.group_by(&:value).values.max_by n, &:size
  end
end

if __FILE__ == $PROGRAM_NAME
  PokerHand.new('Black', '2H 3D 5S 9C KD').vs PokerHand.new('White', '2C 3H 4S 8C AH')
  PokerHand.new('Black', '2H 4S 4C 2D 4H').vs PokerHand.new('White', '2S 8S AS QS 3S')
  PokerHand.new('Black', '2H 3D 5S 9C KD').vs PokerHand.new('White', '2C 3H 4S 8C KH')
  PokerHand.new('Black', '2H 3D 5S 9C KD').vs PokerHand.new('White', '2D 3H 5C 9S KH')
end