make_change.rb

## Ways to make change
#
# Submitter: Paul Bergeron - paul.d.bergeron@gmail.com
# Website:   pauldbergeron.com
# Github:    https://github.com/dinedal
# Location:  San Francisco - CA
#
# Recursive solution, will blow the stack with large values, but memoizes so it trades
# memory for increased speed.

coin_types = gets.split(", ").map(&:to_i)
make_change_val = gets.to_i

class ChangeMaker
  def initialize
    @memo = {}
  end

  def make_change(coins, val)
    # Check stop conditions
    if coins.length == 0   # No coins to deal with, no ways to make change
      0
    elsif coins.length == 1 # One coin
      val % coins[0] == 0 ? 1 : 0 # If it's divisable by the coin, it's one way, else no ways
    else
      # Real meat of the loop, check the this coin against combinations of other coins
      number_of_ways = 0
      this_coin = coins.first
      other_coins = coins[1..-1]

      i = 0
      while(val - i * this_coin >= 0)  # iterate, each step of the coin's value
        args = [other_coins, val - i * this_coin]  # args is the memoized key
        # prefer the memo, otherwise count what other ways the other coins can make change
        number_of_ways += (@memo[args] ||= make_change(*args))
        i += 1
      end

      number_of_ways
    end
  end
end

cm = ChangeMaker.new

puts cm.make_change(coin_types.sort.uniq, make_change_val)

Nice code! If you rename the gist filename to .rb it will look even prettier! :)