who_is_the_killer.rb

#
# #####################################
# Who is the killer?
# #####################################
#
# Handel has been killed and Beethoven is on the case. He has
# interviewed the four suspects and their statements are shown below.
# Each suspect has said two sentences. One sentence of each suspect is a
# lie and one sentence is the truth. Help Beethoven figure out who the
# killer is.
#
# Joplin:   I did not kill Handel. Either Grieg is the killer or none of us is.
# Grieg:    I did not kill Handel. Gershwin is the killer.
# Strauss:  I did not kill Handel. Grieg is lying when he says Gershwin is the killer.
# Gershwin: I did not kill Handel. If Joplin did not kill him, then Grieg did.
#
#
# Fact: each person have made a true and false statement.
# Fact: each persons first statement is that they did not kill Handel. 
#
# therefore...
# Fact: killers second statement must be true
# Fact: non-killers second statement must be false
#
#
#

def reveal_killers
  puts Joplin.killer? ?   "Joplin:    killer!" : "Joplin:    is innocent"
  puts Grieg.killer? ?    "Grieg:     killer!" : "Grieg:     is innocent"
  puts Strauss.killer? ?  "Strauss:   killer!" : "Strauss:   is innocent"
  puts Gershwin.killer? ? "Gershwin   killer!" : "Gershwin:  is innocent"
end

def make_assumption
  assumtion = [Joplin, Grieg, Strauss, Gershwin][rand(4)]
  puts "assuming #{ assumtion.to_s } is the killer..."
  assumtion.instance_eval{
    def killer?
      true
    end
  }
  assumtion.results_of_assumtion
end

class Suspect
  def self.killer?
    @killer ||= self.statement == true
  end  
  
  def self.results_of_assumtion
    begin
      reveal_killers
    rescue
      puts "wait a second... this logic is broken. he cannot be the killer. try someone else...\n\n"
      self.instance_eval{
        def killer?
          false
        end
      }
      make_assumption
    end
  end
  
end

#### Suspects

class Joplin < Suspect
  def self.statement
    Grieg.killer? || ( !Grieg.killer? && !Strauss.killer? && !Gershwin.killer? && !Joplin.killer? )
  end
end

class Grieg < Suspect
  def self.statement
    Gershwin.killer?
  end
end

class Strauss < Suspect
  def self.statement
    Grieg.statement == false
  end
end

class Gershwin < Suspect
  def self.statement
    Joplin.killer? || Grieg.killer?
  end  
end

make_assumption