54 lines
1.5 KiB
Elixir
54 lines
1.5 KiB
Elixir
defmodule Day1 do
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def part1(input) do
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lines = String.split(input)
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ints = Enum.map(lines, fn line -> String.to_integer(line) end)
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pairs = all_pairs(ints)
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[{a, b}] = Enum.filter(pairs, fn {a, b} -> a + b == 2020 end)
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a * b
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end
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defp all_pairs(list) do
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Enum.reduce(0..(length(list) - 1), [], fn idx, pairs ->
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item = Enum.at(list, idx)
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other_items = Enum.slice(list, (idx + 1)..(length(list) - 1))
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new_pairs = Enum.map(other_items, fn elt -> {item, elt} end)
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pairs ++ new_pairs
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end)
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end
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# Wow, I'm out of shape when it comes to making sets recursively!
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def part2(input) do
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lines = String.split(input)
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ints = Enum.map(lines, &String.to_integer/1)
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pairs = all_triples(ints)
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[{a, b, c}] = Enum.filter(pairs, fn {a, b, c} -> a + b + c == 2020 end)
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a * b * c
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end
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defp all_triples(list) do
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Enum.reduce(0..(length(list) - 1), [], fn idx, triples ->
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item = Enum.at(list, idx)
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pairs = all_pairs(Enum.slice(list, (idx + 1)..(length(list) - 1)))
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new_triples = Enum.map(pairs, fn {a, b} -> {item, a, b} end)
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triples ++ new_triples
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end)
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end
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defp combinations(list, size) do
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indices = 0..(length(list) - 1)
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Enum.zip(for _ <- 1..size, do: indices)
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|> IO.inspect()
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|> Enum.filter(fn idxs -> length(Enum.uniq(Tuple.to_list(idxs))) == size end)
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|> Enum.map(fn idxs ->
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for i <- 0..(size - 1) do
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elem(idxs, i)
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end
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end)
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end
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end
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input = File.read!("input.txt")
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IO.inspect(Day1.part1(input))
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IO.inspect(Day1.part2(input))
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