Coin Change Problem solved in Ruby using While and Until. US Coins. Requires RSpec. To run: $ rspec change_spec.rb Not the fewest lines possible but definitely easy for others to understand. ;-)

change_spec.rb

class Change
  def change(amount)
    coins = []
    remaining_amount = amount
    while remaining_amount != 0
      coin = get_highest_coin(remaining_amount)
      coins << coin
      remaining_amount = remaining_amount - coin
    end
    coins
  end

  def get_highest_coin(amount)
      available_coins = [100,25,10,5,1]
      index = 0
      coin = available_coins[index]
      until amount >= coin
         index = index + 1
         coin = available_coins[index]
      end
      puts "Amount: #{amount} | Coin: #{coin}"
      coin
  end
end

describe Change do

  it "returns the highest coin given the amount 30 should be 25" do
      expect(subject.get_highest_coin(30)).to eq 25
  end

  it "returns the highest coin given the amount 11 should be 10" do
      expect(subject.get_highest_coin(11)).to eq 10
  end

  it "returns the highest coin given the amount 7 should be 5" do
      expect(subject.get_highest_coin(7)).to eq 5
  end

  it "returns the highest coin given the amount 1 should be 1" do
      expect(subject.get_highest_coin(1)).to eq 1
  end

  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
end