2023 Day5 part 2
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1 changed files with 40 additions and 22 deletions
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@ -8,35 +8,53 @@ defmodule Day5 do
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def lookup([], item), do: item
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def lookup([{source, dest} | rest], item) do
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def lookup([{source, offset} | rest], item) do
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if item in source do
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dest + item - source.first
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item + offset
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else
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lookup(rest, item)
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end
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end
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def part2(_input) do
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:ok
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def part2({seeds, maps}) do
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seed_ranges =
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seeds
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|> Enum.chunk_every(2)
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|> Enum.map(fn [start, len] -> start..(start + len - 1) end)
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maps
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|> Enum.reduce(seed_ranges, &process_ranges/2)
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|> Enum.min_by(& &1.first)
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|> then(& &1.first)
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end
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# dest range start
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# source range start
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# length
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# no map = same number
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def process_ranges(_map_ranges, []), do: []
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# could brute force it by building a map
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# but the ranges are huge, so that won't work
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# actually need to find if in a range
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def process_ranges(map_ranges, [item_range | rest]) do
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overlap =
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Enum.find(map_ranges, fn {source, _offset} -> not Range.disjoint?(source, item_range) end)
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case overlap do
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nil ->
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[item_range | process_ranges(map_ranges, rest)]
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{source, offset} ->
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to_shift = max(source.first, item_range.first)..min(source.last, item_range.last)
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# ugh. Tidy this up
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remainders =
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List.flatten([
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if(item_range.first < source.first,
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do: [item_range.first..(source.first - 1)],
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else: []
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),
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if(item_range.last > source.last, do: [(source.last + 1)..item_range.last], else: [])
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])
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[Range.shift(to_shift, offset) | process_ranges(map_ranges, remainders ++ rest)]
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end
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end
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# given a source
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# 1) check if it's in a range
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# 2) if it is, follow the rule, otherwise same number
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# 3) follow path
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# well it's mlogn but it should work?
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# store a list of ranges
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# check each seed to see if it's in the range, if it is, follow it, if not, name number
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# we could binsearch the range but let's just do it linear for now, there aren't many seeds
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def input do
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with [input_filename] <- System.argv(),
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{:ok, input} <- File.read(input_filename) do
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@ -51,7 +69,7 @@ defmodule Day5 do
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|> Enum.map(&String.to_integer/1)
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|> Enum.chunk_every(3)
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|> Enum.map(fn [dest, source, offset] ->
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{source..(source + offset), dest}
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{source..(source + offset), dest - source}
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end)
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end)
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@ -80,7 +98,7 @@ defmodule Day5 do
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defp run_with_timer(part, fun) do
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{time, result} = :timer.tc(fun)
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IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
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IO.puts("#{inspect(result)}\n")
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IO.puts("#{inspect(result, charlists: :as_lists)}\n")
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end
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defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
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@ -92,4 +110,4 @@ defmodule Day5 do
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end
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end
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# Day5.run()
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Day5.run()
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