2023 Day5 Part 1

2023/day5.exs

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+#!/usr/bin/env elixir
+defmodule Day5 do
+  def part1({seeds, maps}) do
+    seeds
+    |> Enum.map(fn seed -> Enum.reduce(maps, seed, &lookup/2) end)
+    |> Enum.min()
+  end
+
+  def lookup([], item), do: item
+
+  def lookup([{source, dest} | rest], item) do
+    if item in source do
+      dest + item - source.first
+    else
+      lookup(rest, item)
+    end
+  end
+
+  def part2(_input) do
+    :ok
+  end
+
+  # dest range start
+  # source range start
+  # length
+  # no map = same number
+
+  # could brute force it by building a map
+  # but the ranges are huge, so that won't work
+  # actually need to find if in a range
+
+  # given a source
+  # 1) check if it's in a range
+  # 2) if it is, follow the rule, otherwise same number
+  # 3) follow path
+  # well it's mlogn but it should work?
+  # store a list of ranges
+  # check each seed to see if it's in the range, if it is, follow it, if not, name number
+  # we could binsearch the range but let's just do it linear for now, there aren't many seeds
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      ["seeds: " <> seeds | maps] = String.split(input, "\n\n")
+      seeds = seeds |> String.split() |> Enum.map(&String.to_integer/1)
+
+      maps =
+        Enum.map(maps, fn line ->
+          [_header, _map | items] = String.split(line)
+
+          items
+          |> Enum.map(&String.to_integer/1)
+          |> Enum.chunk_every(3)
+          |> Enum.map(fn [dest, source, offset] ->
+            {source..(source + offset), dest}
+          end)
+        end)
+
+      {seeds, maps}
+    else
+      _ -> :error
+    end
+  end
+
+  #######################
+  # HERE BE BOILERPLATE #
+  #######################
+
+  def run do
+    case input() do
+      :error -> print_usage()
+      input -> run_parts_with_timer(input)
+    end
+  end
+
+  defp run_parts_with_timer(input) do
+    run_with_timer(1, fn -> part1(input) end)
+    run_with_timer(2, fn -> part2(input) end)
+  end
+
+  defp run_with_timer(part, fun) do
+    {time, result} = :timer.tc(fun)
+    IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
+    IO.puts("#{inspect(result)}\n")
+  end
+
+  defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
+  defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
+  defp format_time(μsec), do: "#{μsec / 1_000_000}s"
+
+  defp print_usage do
+    IO.puts("Usage: elixir day5.exs input_filename")
+  end
+end
+
+# Day5.run()