23 lines
817 B
Elixir
23 lines
817 B
Elixir
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defmodule PrimeFactors do
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@doc """
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Compute the prime factors for 'number'.
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The prime factors are prime numbers that when multiplied give the desired
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number.
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The prime factors of 'number' will be ordered lowest to highest.
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"""
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@spec factors_for(pos_integer) :: [pos_integer]
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def factors_for(number), do: do_factors_for(number)
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defp do_factors_for(number, acc \\ [], divisor \\ 2)
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defp do_factors_for(1, acc, _divisor), do: Enum.reverse(acc)
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defp do_factors_for(number, acc, divisor) when rem(number, divisor) == 0 do
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case divisor < trunc(number ** 0.5) + 1 do
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true -> do_factors_for(div(number, divisor), [divisor | acc])
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false -> Enum.reverse([divisor | acc])
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end
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end
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defp do_factors_for(number, acc, divisor), do: do_factors_for(number, acc, divisor + 1)
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end
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