67 lines
1.5 KiB
Elixir
67 lines
1.5 KiB
Elixir
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defmodule Day6 do
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def part1 do
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File.read!("lib/day6/input.txt")
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|> parse_orbits()
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|> total_orbits()
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end
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def part2 do
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# orbits = parse_orbits("COM)B\nB)C\nC)D\nD)E\nE)F\nB)G\nG)H\nD)I\nE)J\nJ)K\nK)L\nK)YOU\nI)SAN")
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orbits =
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File.read!("lib/day6/input.txt")
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|> parse_orbits()
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you_path = path_to_root(orbits, "YOU") |> Enum.reverse()
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san_path = path_to_root(orbits, "SAN") |> Enum.reverse()
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{rem1, rem2} = remaining_after_lowest_common_element(you_path, san_path)
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length(rem1) - 1 + (length(rem2) - 1)
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end
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def parse_orbits(str) do
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str
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|> String.split("\n")
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|> Enum.map(fn line -> String.split(line, ")") end)
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|> Enum.reduce(%{}, fn [orbitted, object], orbits ->
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Map.put(orbits, object, orbitted)
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end)
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end
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def total_orbits(orbits) do
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orbits
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|> Map.keys()
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|> Enum.reduce(0, fn object, acc ->
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acc + orbit_count(orbits, object)
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end)
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end
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def orbit_count(orbits, object) do
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case Map.get(orbits, object) do
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nil ->
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0
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orbitted ->
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1 + orbit_count(orbits, orbitted)
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end
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end
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def path_to_root(graph, start) do
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case Map.get(graph, start) do
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nil ->
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[]
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parent ->
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[parent | path_to_root(graph, parent)]
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end
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end
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def remaining_after_lowest_common_element([_, one | _] = list1, [_, two | _] = list2)
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when one != two do
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{list1, list2}
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end
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def remaining_after_lowest_common_element([_ | rest1], [_ | rest2]) do
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remaining_after_lowest_common_element(rest1, rest2)
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end
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end
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