Countdown: an attempt at creating a 'Countdown'

countdown.rb

# Countdown.rb
# 
# A lame attempt by someone who last used Ruby in the Paleolithic period (I think Perl was around then) to solve the Countdown problem ( http://rubyquiz.com/quiz7.html ). Bad habits from Python, PHP and various things are included.
# 
# Attempted as a follow-up to the ScotRUG user group meeting coding kata.
# 
# Will generate solutions for any combination of six integers.
# 
# ©2012 Graeme West <[email protected]>
# Licensed under the Apache 2.0 licence ( http://www.apache.org/licenses/LICENSE-2.0 ). If you're into that kind of thing.

numbers = [100, 8, 4, 6, 7, 5]
operators = ["*","/","+","-"]

target = 108

class Array
  def random_element
    self[rand(length)]
  end
end


# A class to represent a possible result
class CountUp
  attr_accessor :expression, :total, :delta

    def initialize(expression, total, delta)
      @expression = expression
      @total = total
      @delta = delta
    end
    
    def to_s
        "Expression: %s\tTotal: %s\tDelta: %s" % [@expression, @total, @delta]
      end
end


def assemble_expressions(numbers,operators,target)
    haystack= []
    (2..6).each do |num_terms|
      combs = numbers.permutation(num_terms).to_a
      operator_combs = operators.permutation((num_terms - 1)).to_a

        combs.uniq.each do |comb|
          operator_combs.each do | operator_comb |
            expr = comb[0].to_s()
            comb[1..-1].each_with_index do |this_term, i|
              expr += " " + operator_comb[i].to_s() + " " + this_term.to_s()
            end

            expr_total = eval(expr)
            delta = target - expr_total
            p = CountUp.new(expr, expr_total.to_s(), delta)
            
            # 'haystack' should now contain every possible combination of operator and terms.
            haystack << p
            puts p.to_s() + "\n" # output them so that we can test the algorithm. 27480 lines, wahey!
          end
        end      
    end
    
    return haystack
#    puts haystack.to_s()   # you might want to output it here I suppose.
end

results = assemble_expressions(numbers,operators,target)

# Pseudo-ruby-or-python-or-something code for cleanup and validation follows below. It's just a memory aide for when I actually write this.
# 
# needles = []
# results.each do {|i| return i if i.delta = 0}
# if needles.length > 0:
#   puts needles
#   exit
# else:     # show the top 5 closest matches
#   results.sort(delta).slice(:5)