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Contents
defmodule Change do
@doc """
Determine the least number of coins to be given to the user such
that the sum of the coins' value would equal the correct amount of change.
It returns :error if it is not possible to compute the right amount of coins.
Otherwise returns the tuple {:ok, map_of_coins}
## Examples
iex> Change.generate(3, [5, 10, 15])
:error
iex> Change.generate(18, [1, 5, 10])
{:ok, %{1 => 3, 5 => 1, 10 => 1}}
"""
@spec generate(integer, list) :: {:ok, map} | :error
def generate(amount, values) do
values |> Enum.sort(&(&2 < &1)) |> generate(amount, %{})
end
defp generate(_, 0, acc), do: {:ok, acc}
defp generate([], _, _), do: :error
defp generate(values = [h | t], amount, acc) do
if amount >= h && divisible?(amount - h, values) do
generate(values, amount - h, Map.update(acc, h, 1, &(&1 + 1)))
else
generate(t, amount, Map.put_new(acc, h, 0))
end
end
defp divisible?(num, values) do
Enum.any?(values, &(rem(num, &1) == 0))
end
end
Version data entries
131 entries across 131 versions & 1 rubygems