combo_grader.rb

combo_grader.rb

# problem statement: https://ioi2018.jp/wp-content/tasks/contest1/combo.pdf
# usage: ruby combo_grader.rb "your program"
class ComboGrader
  KEYS = %w[A B X Y].freeze
  COMMAND_LENGTH = 100
  QUERY_LENGTH_LIMIT = COMMAND_LENGTH * 4
  QUERY_LIMIT = 103

  def run(program)
    @program = IO.popen(program, mode = "r+")

    mystery_command = generate(COMMAND_LENGTH)

    QUERY_LIMIT.times do
      type, contents = fetch_and_parse_query
      if type == '!'
        query_answer(mystery_command, contents)
      else
        @program.puts query_ask(mystery_command, contents)
      end
    end

    print_and_exit(['Query limit exceeded'])
  end

  private

  def print_and_exit(messages = [], success = false)
    STDERR.puts messages.join("\n")
    @program.close

    exit(success ? 0 : 1)
  end

  def query_answer(mystery_command, query)
    if mystery_command == query
      print_and_exit(['Congratulations!', "Command was #{query} as you answered."], true)
    else
      print_and_exit(['Wrong answer.', "Command was #{mystery_command} but you answered #{query}."])
    end
  end

  def query_ask(mystery_command, query)
    if query.length > QUERY_LENGTH_LIMIT
      print_and_exit(['Query too long.', "Your query #{query} is too long: over #{QUERY_LENGTH_LIMIT} characters."])
    end

    1.upto(mystery_command.length).each do |prefix_length|
      prefix = mystery_command.slice(0, prefix_length)
      unless query.include?(prefix)
        return prefix_length-1
      end
    end
    mystery_command.length
  end

  def fetch_and_parse_query
    query_type, contents = @program.gets.chomp.split(' ')
    print_and_exit(['invalid query']) unless %w[? !].include?(query_type)
    [query_type, contents]
  end

  def generate(length)
    first_key = KEYS.sample
    sequence_keys = KEYS - [first_key]
    first_key + Array.new(length-1).map { sequence_keys.sample }.join
  end
end

ComboGrader.new.run(ARGV.first)