2023/day3.exs

@@ -1,90 +0,0 @@
-#!/usr/bin/env elixir
-defmodule Day3 do
-  def part1(_input) do
-    # for each number, check around its edges to see if there's a symbol
-    fn {{x, y}, number, length}, acc ->
-      top = for x <- (x - 1)..(x + length), do: {x, y - 1}
-      bottom = for x <- (x - 1)..(x + length), do: {x, y + 1}
-      box = [{x - 1, y}, {x + length, y}] ++ top ++ bottom
-      if part_number?(box), do: [number | acc], else: acc
-    end
-    |> :ets.foldl(_acc = [], :numbers)
-    |> Enum.sum()
-  end
-
-  def part_number?([]), do: false
-
-  def part_number?([coord | rest]) do
-    case :ets.lookup(:symbols, coord) do
-      [_symbol] -> true
-      [] -> part_number?(rest)
-    end
-  end
-
-  def part2(_input) do
-    :ok
-  end
-
-  def input do
-    with [input_filename] <- System.argv(),
-         {:ok, input} <- File.read(input_filename) do
-      :ets.new(:numbers, [:named_table])
-      :ets.new(:symbols, [:named_table])
-      parse_schematic(input, _x = 0, _y = 0)
-    else
-      _ -> :error
-    end
-  end
-
-  def parse_schematic("", _x, _y), do: :ok
-  def parse_schematic("." <> rest, x, y), do: parse_schematic(rest, x + 1, y)
-  def parse_schematic("\n" <> rest, _x, y), do: parse_schematic(rest, 0, y + 1)
-
-  def parse_schematic(<<digit::utf8>> <> rest, x, y) when digit in ?0..?9 do
-    {number, length, rest} = take_digits(<<digit::utf8>> <> rest, "", 0)
-    :ets.insert(:numbers, {{x, y}, number, length})
-    parse_schematic(rest, x + length, y)
-  end
-
-  def parse_schematic(<<symbol::utf8>> <> rest, x, y) do
-    :ets.insert(:symbols, {{x, y}, <<symbol::utf8>>})
-    parse_schematic(rest, x + 1, y)
-  end
-
-  def take_digits(<<digit::utf8>> <> rest, digits, count) when digit in ?0..?9,
-    do: take_digits(rest, digits <> <<digit::utf8>>, count + 1)
-
-  def take_digits(rest, digits, count), do: {String.to_integer(digits), count, rest}
-
-  #######################
-  # 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 day3.exs input_filename")
-  end
-end
-
-# Day3.run()

2023/day4.exs

@@ -2,28 +2,35 @@
 defmodule Day4 do
   def part1(input) do
     input
-    |> Enum.map(fn 0 -> 0; num_winners -> 2 ** (num_winners - 1) end)
+    |> Enum.map(fn {_id, num_winners} ->
+      case num_winners do
+        0 -> 0
+        num_winners -> 2 ** (num_winners - 1)
+      end
+    end)
     |> Enum.sum()
   end
 
   def part2(input) do
     input
-    |> Enum.map(fn num_winners -> {_num_copies = 1, num_winners} end)
+    |> Enum.sort_by(fn {id, _num_winners} -> id end)
+    |> Enum.map(fn {_id, num_winners} -> {_num_copies = 1, num_winners} end)
     |> copy()
+    |> Enum.map(fn {num_copies, _num_winners} -> num_copies end)
     |> Enum.sum()
   end
 
   def copy([]), do: []
 
-  def copy([{num_copies, num_winners} | rest]) do
+  def copy([{above_num_copies, num_winners} = current | rest]) do
     {to_copy, left_alone} = Enum.split(rest, num_winners)
 
     copied =
-      Enum.map(to_copy, fn {child_num_copies, num_winners} ->
-        {num_copies + child_num_copies, num_winners}
+      Enum.map(to_copy, fn {below_num_copies, num_winners} ->
+        {above_num_copies + below_num_copies, num_winners}
       end)
 
-    [num_copies | copy(copied ++ left_alone)]
+    [current | copy(copied ++ left_alone)]
   end
 
   def input do
@@ -32,12 +39,16 @@ defmodule Day4 do
       input
       |> String.split("\n", trim: true)
       |> Enum.map(fn line ->
-        [_card_id, winning, have] = String.split(line, [": ", " | "])
+        [card_id, winning, have] = String.split(line, [": ", " | "])
+        ["Card", id] = String.split(card_id, " ", trim: true)
 
-        winning = winning |> String.split(" ", trim: true) |> MapSet.new()
-        have = have |> String.split(" ", trim: true) |> MapSet.new()
+        [winning, have] =
+          for cards <- [winning, have],
+              do: cards |> String.split(" ", trim: true) |> MapSet.new(&String.to_integer/1)
 
-        MapSet.intersection(winning, have) |> MapSet.size()
+        num_winners = MapSet.intersection(winning, have) |> MapSet.size()
+
+        {String.to_integer(id), num_winners}
       end)
     else
       _ -> :error