74 lines
1.5 KiB
Elixir
74 lines
1.5 KiB
Elixir
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defmodule Day1 do
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@example_1 """
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1721
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979
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366
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299
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675
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1456
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"""
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def part1(example \\ false) do
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if(example, do: @example_1, else: File.read!("lib/day1/input.txt"))
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(&String.to_integer/1)
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|> all_pairs()
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|> find_sum_to_2020()
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end
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def part2(example \\ false) do
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if(example, do: @example_1, else: File.read!("lib/day1/input.txt"))
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(&String.to_integer/1)
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|> all_triples()
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|> find_sum_to_2020()
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end
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def all_pairs(items) do
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items
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|> Enum.drop(-1)
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|> Enum.with_index()
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|> Enum.flat_map(fn {a, a_index} ->
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{_, rest} = Enum.split(items, a_index + 1)
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Enum.map(rest, fn b ->
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{a, b}
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end)
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end)
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end
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def all_triples(items) do
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items
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|> Enum.drop(-1)
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|> Enum.with_index()
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|> Enum.flat_map(fn {a, a_index} ->
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{_, rest} = Enum.split(items, a_index + 1)
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rest
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|> Enum.drop(-1)
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|> Enum.with_index()
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|> Enum.flat_map(fn {b, b_index} ->
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{_, rest_rest} = Enum.split(rest, b_index + 1)
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Enum.map(rest_rest, fn c ->
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{a, b, c}
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end)
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end)
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end)
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end
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def find_sum_to_2020(groups) do
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Enum.find_value(groups, fn items ->
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list = Tuple.to_list(items)
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if Enum.reduce(list, 0, &(&1 + &2)) == 2020 do
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Enum.reduce(list, 1, &(&1 * &2))
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else
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nil
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end
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end)
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end
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end
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