24 lines
738 B
Elixir
24 lines
738 B
Elixir
defmodule Hailstone do
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require Integer
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def step(1) , do: 0
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def step(n) when Integer.is_even(n), do: div(n,2)
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def step(n) , do: n*3 + 1
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def sequence(n) do
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Stream.iterate(n, &step/1) |> Stream.take_while(&(&1 > 0)) |> Enum.to_list
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end
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def run do
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seq27 = sequence(27)
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len27 = length(seq27)
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repr = String.replace(inspect(seq27, limit: 4) <> inspect(Enum.drop(seq27,len27-4)), "][", ", ")
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IO.puts "Hailstone(27) has #{len27} elements: #{repr}"
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{len, start} = Enum.map(1..100_000, fn(n) -> {length(sequence(n)), n} end) |> Enum.max
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IO.puts "Longest sequence starting under 100000 begins with #{start} and has #{len} elements."
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end
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end
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Hailstone.run
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