42 lines
1.1 KiB
Elixir
42 lines
1.1 KiB
Elixir
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defmodule PerfectNumbers do
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@doc """
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Determine the aliquot sum of the given `number`, by summing all the factors
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of `number`, aside from `number` itself.
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Based on this sum, classify the number as:
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:perfect if the aliquot sum is equal to `number`
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:abundant if the aliquot sum is greater than `number`
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:deficient if the aliquot sum is less than `number`
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"""
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@spec classify(number :: integer) :: {:ok, atom} | {:error, String.t()}
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def classify(number) when number <= 0, do: {:error, "Classification is only possible for natural numbers."}
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def classify(1), do: {:ok, :deficient}
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def classify(number) do
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sum =
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number
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|> divisors()
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|> Enum.sum()
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cond do
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sum == number ->
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{:ok, :perfect}
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sum > number ->
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{:ok, :abundant}
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sum < number ->
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{:ok, :deficient}
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end
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end
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defp divisors(number) do
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for i <- 1..round(number ** 0.5), reduce: [] do
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acc -> if rem(number, i) == 0, do: [i, div(number, i) | acc], else: acc
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end
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|> Enum.uniq()
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|> Enum.sort()
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|> Enum.drop(-1)
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end
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end
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