Coin Change Problem Single Method. Solved in Ruby. Nested until loops. ( requires RSpec) Available coins are USD: http://en.wikipedia.org/wiki/Coins_of_the_United_States_dollar ;-)

change_spec.rb

class Change
  def change(amount)
    available_coins = [100,50,25,10,5,1] # http://en.wikipedia.org/wiki/Coins_of_the_United_States_dollar
    coins = []
    index = 0
    coin = available_coins[index]
    remaining_amount = amount
    until remaining_amount == 0
      until remaining_amount >= coin
         index = index + 1
         coin = available_coins[index]
      end
      puts "Amount: #{remaining_amount} | Coin: #{coin}"
      coins << coin
      remaining_amount = remaining_amount - coin
    end
    coins
  end
end

describe Change do

  it "returns [1] for 1" do
    expect(subject.change(1)).to eq [1]
  end

  it "returns [1, 1, 1, 1] for 4" do
    expect(subject.change(4)).to eq [1,1,1,1]
  end

  it "returns [5, 1] for 6" do
    expect(subject.change(6)).to eq [5,1]
  end

  it "returns [25, 10, 10, 1, 1, 1] for 48" do
    expect(subject.change(48)).to eq [25,10,10,1,1,1]
  end

  it "returns [100, 25, 10, 5, 1, 1] for 142" do
    expect(subject.change(142)).to eq [100,25,10,5,1,1]
  end

  it "returns [100,100,50,25,10,1] for 286" do
    expect(subject.change(286)).to eq [100,100,50,25,10,1]
  end
end