From: Andreas Launila <ruby-talk@...>
Date: 2008-11-07T00:51:24+09:00
Subject: Re: Combination of numbers in an array that add up to x

Hae Lee wrote:
> Andreas Launila wrote:
>> The simplest way to solve this problem in Gecode/R is probably to use
>> set variables:
>>
>> [...]
> 
> Hi there; thanks so much!  Qq (quick question): How would I modify this 
> so that it lists each possible combination surrounded within their own 
> bracket sets? 
> 

That is covered in
http://gecoder.rubyforge.org/documentation/searching_for_solutions.html
. There doesn't exist a convenience method for it, so one has to
formulate the problem as a class:

  require 'rubygems'
  require 'gecoder'

  class ArraySumProblem
    include Gecode::Mixin

    def initialize
      weights = [2429.63, 497.87, 51.96, 59.43, 138.4, 66.22, 28.74,
        1.75, 2075.13, 556.14, 112.56, 116.5, 84.41, 55.97, 139.07,
        24.46]
      # Convert to integers.
      weights.map!{ |x| (x*100).floor }

      selected_weights_is_a set_var([], weights)
      selected_weights.sum.must == 343578

      branch_on selected_weights
    end
  end

  ArraySumProblem.new.each_solution do |solution|
    p solution.selected_weights.value.map{ |x| x.to_f / 100 }
  end

Output:

  [1.75, 112.56, 116.5, 138.4, 139.07, 497.87, 2429.63]
  [24.46, 28.74, 51.96, 59.43, 66.22, 138.4, 139.07, 497.87, 2429.63]

If you are planning to solve several instances of the problem then you
probably want to modify the above so that the weights and target are
sent in through the constructor.

-- 
Andreas Launila