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defmodule Day22 do
def part1(data, n \\ 2000) do
data
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.map(&(secret_numbers(&1, n)))
|> Enum.map(&hd/1)
|> Enum.sum()
end
defp secret_numbers(v, n) do
for _ <- 1..n, reduce: [v] do
v ->
[(v |> hd() |> change_value(6) |> change_value(-5) |> change_value(11)) | v]
end
end
defp change_value(v, shift) do
v
|> Bitwise.bsl(shift)
|> Bitwise.bxor(v)
|> Integer.mod(16777216)
end
def part2(data, n \\ 2000) do
data
|> String.split("\n", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.map(&(secret_numbers(&1, n)))
|> Enum.map(&(sequences(&1, 10)))
|> Enum.reduce(%{}, fn s, acc ->
Map.merge(acc, s, fn _k, v1, v2 -> v1 + v2 end)
end)
|> Map.values()
|> Enum.max()
end
defp sequences(vs, m) do
vs
|> Enum.map(&Integer.mod(&1, m))
|> Enum.chunk_every(5, 1, :discard) # performance here could be improved
|> Enum.map(fn chunk -> {diffs(chunk), hd(chunk)} end)
|> Map.new()
end
defp diffs(vs) do
vs
|> Enum.chunk_every(2, 1, :discard)
|> Enum.map(fn [a, b] -> a - b end)
|> List.to_tuple()
end
end
data = IO.read(:stdio, :eof)
{time1, ans1} = :timer.tc(fn -> Day22.part1(data) end)
IO.puts("Time : #{time1 / 1000000}")
IO.puts("Answer: #{ans1}") # 19822877190
{time2, ans2} = :timer.tc(fn -> Day22.part2(data) end)
IO.puts("Time : #{time2 / 1000000}")
IO.puts("Answer: #{ans2}") # 2277
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