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Contents
defmodule PerfectNumbers do
@doc """
Determine the aliquot sum of the given `number`, by summing all the factors
of `number`, aside from `number` itself.
Based on this sum, classify the number as:
:perfect if the aliquot sum is equal to `number`
:abundant if the aliquot sum is greater than `number`
:deficient if the aliquot sum is less than `number`
"""
@spec classify(number :: integer) :: ({ :ok, atom } | { :error, String.t() })
def classify(number) when number < 1, do: { :error, "Classification is only possible for natural numbers." }
def classify(number) do
{ :ok, number |> aliquot_sum |> do_classify(number) }
end
defp do_classify(aliquot, aliquot), do: :perfect
defp do_classify(aliquot, number) when aliquot > number, do: :abundant
defp do_classify(_, _), do: :deficient
defp aliquot_sum(number) do
number
|> factors
|> Enum.reject(&(&1 == number))
|> Enum.sum
end
defp factors(number), do: factors(number, div(number, 2))
defp factors(1, _), do: [1]
defp factors(_, 1), do: [1]
defp factors(number, i) when rem(number, i) == 0, do: [i | factors(number, i-1)]
defp factors(number, i), do: factors(number, i-1)
end
Version data entries
195 entries across 195 versions & 1 rubygems