Whole Number Combinations == 100

combinator.rb

#! /usr/bin/env ruby

def combinator(answer, known_val, current_val, arr)
  nums = arr.dup
  if nums.length.zero?
    puts answer if known_val+current_val == 100
    return
  end

  next_num = nums.shift

  #add
  combinator("#{answer}+#{next_num}", known_val+current_val, next_num, nums)

  #sub
  combinator("#{answer}-#{next_num}", known_val+current_val, -next_num, nums)

  #concat
  combinator("#{answer}#{next_num}", known_val, (current_val.to_s + next_num.to_s).to_i, nums)
end

combinator('1', 0, 1, [2,3,4,5,6,7,8,9])