Add 2015 Day4

2015/day1.exs

@@ -0,0 +1,52 @@
+defmodule Day1 do
+  def part1(<<>>), do: 0
+  def part1(<<?(, rest::binary>>), do: 1 + part1(rest)
+  def part1(<<?), rest::binary>>), do: -1 + part1(rest)
+
+  def part2(input), do: find_basement(input, _floor = 0, _pos = 1)
+
+  def find_basement(<<?), _::binary>>, 0, pos), do: pos
+  def find_basement(<<?), rest::binary>>, floor, pos), do: find_basement(rest, floor - 1, pos + 1)
+  def find_basement(<<?(, rest::binary>>, floor, pos), do: find_basement(rest, floor + 1, pos + 1)
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+    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("#{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 day1.exs input_filename")
+  end
+end
+
+Day1.run()

2015/day2.exs

@@ -0,0 +1,66 @@
+defmodule Day2 do
+  def part1(input) do
+    input
+    |> Enum.map(fn [x, y, z] ->
+      a = x * y
+      b = x * z
+      c = y * z
+      min = Enum.min([a, b, c])
+      2 * (a + b + c) + min
+    end)
+    |> Enum.sum()
+  end
+
+  def part2(input) do
+    input
+    |> Enum.map(fn box ->
+      [x, y, z] = Enum.sort(box)
+      2 * (x + y) + x * y * z
+    end)
+    |> Enum.sum()
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split(["\n", "x"], trim: true)
+      |> Enum.map(&String.to_integer/1)
+      |> Enum.chunk_every(3)
+    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("#{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 day2.exs input_filename")
+  end
+end
+
+Day2.run()

2015/day3.exs

@@ -0,0 +1,67 @@
+defmodule Day3 do
+  def part1(input), do: move(input, MapSet.new([{0, 0}]), {0, 0})
+
+  def move(<<?<, rest::binary>>, houses, {x, y}), do: deliver(rest, houses, {x - 1, y})
+  def move(<<?>, rest::binary>>, houses, {x, y}), do: deliver(rest, houses, {x + 1, y})
+  def move(<<?^, rest::binary>>, houses, {x, y}), do: deliver(rest, houses, {x, y - 1})
+  def move(<<?v, rest::binary>>, houses, {x, y}), do: deliver(rest, houses, {x, y + 1})
+  def move(<<>>, houses, _addr), do: MapSet.size(houses)
+
+  def deliver(moves, houses, addr), do: move(moves, MapSet.put(houses, addr), addr)
+
+  def part2(input), do: move2(input, MapSet.new([{0, 0}]), {0, 0}, {0, 0})
+
+  def move2(<<ms, mb, rest::binary>>, houses, santa, bot) do
+    santa = next(ms, santa)
+    bot = next(mb, bot)
+    move2(rest, MapSet.union(houses, MapSet.new([santa, bot])), santa, bot)
+  end
+
+  def move2(<<>>, houses, _santa, _bot), do: MapSet.size(houses)
+
+  def next(?<, {x, y}), do: {x - 1, y}
+  def next(?>, {x, y}), do: {x + 1, y}
+  def next(?^, {x, y}), do: {x, y - 1}
+  def next(?v, {x, y}), do: {x, y + 1}
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+    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("#{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()

2015/day4.exs

@@ -0,0 +1,50 @@
+defmodule Day4 do
+  def part1(input), do: mine(input, 1, "00000")
+
+  def mine(input, nonce, prefix) do
+    hash = :crypto.hash(:md5, input <> Integer.to_string(nonce)) |> Base.encode16()
+    if String.starts_with?(hash, prefix), do: nonce, else: mine(input, nonce + 1, prefix)
+  end
+
+  def part2(input), do: mine(input, 1, "000000")
+
+  def input do
+    with [input] <- System.argv() do
+      input
+    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("#{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 day4.exs input")
+  end
+end
+
+Day4.run()