adversarial_hangman.rb

require 'open-uri'

# I happened to watch [this video](https://www.youtube.com/watch?v=le5uGqHKll8) and it got
# me thinking about if the executioner cheats by changing the word during the course of the
# game, can the guesser still win?
#
# Results:
# 1: y, 24
# 2: ky, 20
# 3: qqv, 16
# 4: vugg, 15
# 5: huzzy, 15
# 6: clucky, 8
# 7: cupfuls, 6
# 8: buckjump, 5
# 9: boughpots, 5
# 10: backtracks, 3
# 11: clancularly, 3
# 12: structurally, 3
# 13: subculturally, 3
# 14: pharyngobranch, 2
# 15: arthropathology, 2
# 16: astrophotography, 2
# 17: photochromography, 2
# 18: phenylacetaldehyde, 2
# 19: lymphogranulomatous, 2
# 20: cholecystenterostomy, 1
# 21: antimaterialistically, 1
# 22: electroencephalography, 1
# 23: phenolsulphonephthalein, 0
# 24: diphenylaminechlorarsine, 0
# 25: microspectrophotometrical, 0
# 27: electroencephalographically, 0
# 28: antidisestablishmentarianism, 0
# 29: cyclotrimethylenetrinitramine, 0
# 31: dichlorodiphenyltrichloroethane, 0

class Game
  def initialize(word_length, possibilities)
    @word_length = word_length
    @possibilities = possibilities
    @guessed = []
    @board = ("_" * word_length).chars
  end

  def play!
    until complete?
      select_word(make_guess)
    end
    [word, wrong_guesses]
  end
  
  def word
    @board.join
  end

  def wrong_guesses
    (@guessed - @board).count
  end

  def complete?
    !@board.include?("_")
  end

  def outstanding_letters
    ('a'..'z').to_a - @guessed
  end

  def make_guess
    # for each outstanding letter, select the letter which minimizes
    # the number of remaining words if the word does not contain
    # that letter. 
    outstanding_letters.min_by do |letter|
      @possibilities.count do |word|
        !word.include?(letter)
      end
    end
  end

  def update_board(guess)
    @guessed << guess
    # select the letter positions which maximize
    # the number of remaining possibilities
    word, @possibilities = @possibilities
      .group_by { |word| word.chars.map { |c| c == guess ? guess : "_" } }
      .max_by { |_, possibilities| possibilities.size }
    @board = @board.zip(word).map(&:max)
  end
end

URI.open("https://raw.githubusercontent.com/dwyl/english-words/master/words_alpha.txt", &:read)
  .each_line.map(&:chomp)
  .group_by(&:size)
  .sort
  .each do |word_length, possibilities|
    board, score = Game.new(word_length, possibilities).play!
    puts "#{word_length}: #{board}, #{score}"
  end