def change(n, list_of_coins)
  changeHelper(n, list_of_coins, [])
end

def changeHelper(n, list_of_coins, result_list)
  if list_of_coins.empty?
    [result_list]
  elsif n == 0
    [result_list]
  else
    if n >= list_of_coins.first
      changeHelper(n - list_of_coins.first, list_of_coins, result_list << list_of_coins.first) +
        changeHelper(n, list_of_coins[1..list_of_coins.count-1], result_list)
    else
      changeHelper(n, list_of_coins[1..list_of_coins.count-1], result_list)
    end
  end
end