65 lines
1.6 KiB
Elixir
65 lines
1.6 KiB
Elixir
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input = IO.gets("input?")
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|> String.trim
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|> String.split(" ")
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|> Enum.map(fn part ->
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String.to_integer part
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end)
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defmodule Day1_2 do
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def pass(input, state) do
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# pass through the entire list with reduce
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# so we have some kind of state in acc
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result = Enum.reduce(input, state, fn part, acc ->
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case acc do
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# if we already found it, we don't need
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# to keep iterating
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{:ok, res} ->
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{:ok, res}
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# acc grows like this:
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# [0]
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# [0 + first_change | 0]
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# [0 + first_change + second_change |
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# [0 + first_change | 0]], etc
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[current | _rest] ->
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# the head of the list is the current
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# frequency of the device that we'll
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# apply the change to (part)
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new_freq = current + part
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# then we search in the OLD list
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# if we are a member of it
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#
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# if we are, then we are actually the first
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# repeated frequency in the list.
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became_member = Enum.member?(acc, new_freq)
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if became_member do
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# this should make the reduce()
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# call stop creating new frequencies
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# and just returning what it found
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{:ok, new_freq}
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else
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# if we didn't find, we add the new frequency
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# to the list, and keep going.
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[new_freq | acc]
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end
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end
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end)
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case result do
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{:ok, res} -> res
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# if
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_ -> pass(input, result)
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end
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end
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end
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res = Day1_2.pass(input, [0])
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IO.puts "total res: #{inspect res}"
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