The enemy of my enemy of my enemy of my enemy of my enemy of my enemy is Kevin Bacon

kevin_bacon.rb

class Person
  attr_reader :name, :enemies

  def initialize name
    @name = name
    @enemies = []
  end

  def add_enemies enemies
    @enemies.concat enemies
  end
end

people = 100.times.map { |i| Person.new(i.to_s) }
people.each { |person| person.add_enemies people.sample(3) }
people.sample.enemies << Person.new("Kevin Bacon")

enemies = people.sample.enemies
6.times do |i|
  enemies += enemies.flat_map(&:enemies).uniq
end

p enemies.map(&:name).include? "Kevin Bacon"