52 lines
1.1 KiB
Elixir
52 lines
1.1 KiB
Elixir
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defmodule AOC.Day9 do
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use AOC.Day, day: 9
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def parse_input(lines) do
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Enum.map(lines, fn line ->
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line
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|> String.split(" ")
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|> Enum.map(&String.to_integer/1)
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end)
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end
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def part1(histories) do
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histories
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|> Enum.map(&predict_next_value/1)
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|> Enum.sum()
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end
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def part2(histories) do
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Enum.map(histories, &predict_previous_value/1)
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|> Enum.sum()
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end
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def predict_next_value(history) do
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history
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|> generate_differences()
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|> Enum.map(&List.last/1)
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|> Enum.sum()
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end
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def predict_previous_value(history) do
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history
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|> generate_differences()
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|> Enum.map(&List.first/1)
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|> Enum.reduce(&Kernel.-/2)
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end
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def generate_differences(history), do: generate_differences(history, [history])
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def generate_differences(numbers, acc) do
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if Enum.all?(numbers, &(&1 == 0)) do
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acc
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else
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differences =
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numbers
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|> Enum.chunk_every(2, 1, :discard)
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|> Enum.map(fn [val1, val2] -> val2 - val1 end)
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generate_differences(differences, [differences | acc])
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end
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end
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end
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