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Contents
defmodule Prime do
@doc """
Generates the nth prime.
"""
@spec nth(non_neg_integer) :: non_neg_integer
def nth(count) do
if count < 1, do: raise(ArgumentError)
nth(count, 1000)
end
defp nth(count, max) do
primes = primes_to(max)
cond do
Enum.count(primes) < count -> nth(count, max * 4)
true -> Enum.at(primes, count - 1)
end
end
defp primes_to(limit) do
Enum.reduce(2..limit, [], fn number, primes ->
if is_prime?(number, primes), do: [number | primes], else: primes
end)
|> Enum.reverse()
end
defp is_prime?(number, primes) do
Enum.all?(primes, &(rem(number, &1) != 0))
end
end
Version data entries
69 entries across 69 versions & 1 rubygems