Day 3 - Advent of Code 2015

Mix.install([:kino, :benchee])

:ok

Links

• Advent of Code (AoC)
• AoC Puzzle Input
• tylerj GitHub

Prompt

— Day 3: Perfectly Spherical Houses in a Vacuum —

Santa is delivering presents to an infinite two-dimensional grid of houses.

He begins by delivering a present to the house at his starting location, and then an elf at the North Pole calls him via radio and tells him where to move next. Moves are always exactly one house to the north (^), south (v), east (>), or west (<). After each move, he delivers another present to the house at his new location.

However, the elf back at the north pole has had a little too much eggnog, and so his directions are a little off, and Santa ends up visiting some houses more than once.

For example:

• > delivers presents to 2 houses: one at the starting location, and one to the east.
• ^>v< delivers presents to 4 houses in a square, including twice to the house at his starting/ending location.
• ^v^v^v^v^v delivers a bunch of presents to some very lucky children at only 2 houses.

How many houses receive at least one present?

To begin, get your puzzle input.

— Part Two —

The next year, to speed up the process, Santa creates a robot version of himself, Robo-Santa, to deliver presents with him.

Santa and Robo-Santa start at the same location (delivering two presents to the same starting house), then take turns moving based on instructions from the elf, who is eggnoggedly reading from the same script as the previous year.

For example:

• ^v delivers presents to 3 houses, because Santa goes north, and then Robo-Santa goes south.
• ^>v< now delivers presents to 3 houses, and Santa and Robo-Santa end up back where they started.
• ^v^v^v^v^v now delivers presents to 11 houses, with Santa going one direction and Robo-Santa going the other.

This year, how many houses receive at least one present??

Although it hasn’t changed, you can still get your puzzle input.

Input

input = Kino.Input.textarea("Please paste your input file:")

input = input |> Kino.Input.read()

"v>v<vvv<<vv^v<v>vv>v<<<^^^^^<<^<vv>^>v^>^>^>^>^><vvvv<^>^<<^><<<^vvvv>^>^><^v^><^<>^^>^vvv^<vv>>^>^^<>><>^>vvv>>^vv>^<><>^<v^>^>^><vv^vv^>><<^><<v>><>^<^>>vvv>v>>>v<<^<><^<v<>v>^^v^^^<^v^^>>><^>^>v<>^<>>^>^^v^><v<v>>><>v<v^v>^v<>>^><v>^<>v^>^<>^v^^^v^^>>vv<<^^><^<vvv>^>^^<^>>^^^^^v^<v>vv<>>v^v<^v^^<><^<^vv^><>><><>v>vvv^vv^^<<><<vvv><<^v^><v<>vvv^<^>vvvv^>^>>^v^<v^vv<^^v<>v>vv^<>><v<<<^v^<<><v<^<^<><^^^>^>>v>^>v^<>v><^<^<v^>^^vv<^^<>v^v^vv<>>>>v^v<>><^^v>vv^^>v^v>v<vv>>v>><v^v^v>vv>^^>^v><<vv^v^^vv<^v><^<<v<v^>vv^^^<v^>v>v^^^>><^^<v^<^>>v><vv<v^^>^^v>>v^^^<^^v>^v>><^<^<>>v<<^^vv>^^^v<^<^<v<v^^vv>^vv^>>v^><v>><<<>^vv^<^<>v^^<<<v<^>^><><v^^>>^^^<^vv<^^^>><^^v>^^v^<v^v^>^^<v>^<^v<^<<<<^<v^>v^<^^<>^^>^><<>>^v><>><^<v><^^^>>vv>^><vv>^^^^^v^vvv><><^<^>v>v^v^>^><><^<^><>v<<vv<^>><>^v^^v>^<<<>^v^>^<<v^vv<>v^<v^^vv><<v^<>>>^<v>vv>v>>>^<^>><vv<>>>>v<v>>>^v>v><>>vvv<^^><<^>^>v<^vvvv<v><vv<><^^^v^^^>v^v<>v<^^v>>><>v<v^>>v><v^>>^^<v<<<^<v<><^^v><<v^><<<<^vv<^<>^><vv<<<<^>>>^v>^v>vv>^v<>v>v<v><^>>v>>^>^><^<v^v^>^v<><><^^>^<vvvv^^<>^^^>vv^v^v>^v^^v^^v><v^<^<>><^<v>v>>vv<<v>>vvvv<vv><>>^v^>^>>v^v^<<<vv<><v<<>>>^v<<v>^^vv^><>v>^>v><<<<<<<^>^^v^<<^^>>vvv^<><>><>^^v<<vv><^^v<^^><vv>v^>>>v^v><v^v<^>v^><>v<<>v>^^v><<<<><^v^v>>^<>^<<>^<v<<>>v<<>><^<<<<^v>^<^v>v>vv<v<v<<>^>v<^<<>v^<vvvv^>v>><<v><v<>v>v>>v^vvv^^>>>v^<^<<^^<<<><v>v^<<v<<<>v<^^<><v<v^^<v>^>v>>v<>^>^^>>^v<<>v^^^>>>^vv<^v<v>^>v>^><>v^^<>^^v^^vv^<^>^<<>><<^>^v>>><<<vvvv><<><v<^v^v<vvv^<><<^<vv><v^v^v^>v>v^<vvv^><^><^<vv><>>v^>^^^<>><v^<^^^<>v<<v<^v>>>^>>v^><<>vvv><^>>v><v><>v>>^>v><<><<>^<>^^^vv><v^>v^^>>^>^<^v<v<^^<^vvvv>v<v>^>v^>^><^<vvvv><^><><<v<>v<v^><^<v^>^v^^<<<<^><^^<^><>>^v<<^<<^vv>v>>v<^<^vv>><v<vv>v<v<v>^v<>^>v<>^v<<<v>>^^v>>><vvv>v^>^v^v>^^^v<vvvv>><^>vvv^<vv^^vv><<<>v<>v>^<vvv^<^<v<v<^vv^^>>vv^<^^v^><^^^^^v<^<v<^>>>vv^v^>^<v>^<><v^<^v>>><^v^<<v<<v<>v>^v<v^v>>^^v<<v<v<<>>>vv>>^v>>^<<<<^><<<><^^>>v<>^vvvv>v^^^>^^^>^<vvvv><^^v<v<>v<^v^v<<v^^^v^<v<^v>v^^<>^>^<^v>vv<v^vv<^<<>v><<^><><^^v<<><^^><>^v>^<><<^<^^<<>vv<>^^<<^>><<<>>vvv>^>v^^v^><<^>v>^>^<^<<>v<^>vv^v^v<>vv<<v>vv<vv><^>v^<>^vv^v^<v<^>>>>v^v><^<><<>vv^<vvv^>>vvv^>v>>><^^vv<vvvv>v<^<^>>^^>^^vv>>><^v<>^v^<<>v^^^<v>^>>^<^<v>>^v<^^^<v>^v>^>>v<vv>>^<v^<<>>^>>><v>v^<<^<v>>^<<^^<>v<^v<^<>v^v>^^v<vvvv>^vv>vvv>v^<^>><v^^vv<<<^>vvvv<>>^^<>v^<><>v<^<>v<>^>v<>vv<v^v>>v<v<^<v^^v^vv^vvv><^^>v>><>>^<^^<>>^>^<v^>>vvv^v><v>>^>^>v><><<><vv^v>v<>^v<^vv^^^<>^^<<^^^v<>><v<^<^<^<^^><v^v<^>v^>vvvv>^^v^>^<v<^^^>>^<<vv^<><><^^^^<<>^<><v>vv^<><^>^^<>v^<>>>v><>vvvvv>v>v^^>^<<vvvv<>vv>>v<<^<>^^^v^<><>>^<<<v<v<>>>><><v>v<v<>>^>^^^^vv^^<<><^^<<vv<^<>v>vv<v<><<<^<<v<<<<>v<>>^<^>^>><v>v>><^^<>><<<><<><v^^v<<><^<^v<v^><^^v<<>><<<<^>v^<v>><v^><v<vvv>v^v^<v><<>>v<><<v>^<>><>>^><>v^v>v<<>v<>v^^><<>>>v<<>>>>^>v>><v<<>>>vv>v>^<^^^<>v<v>^<^^v^vvv^>vv>^<v><vvvv>^<<>vvv<<<vv>^^<^>^>>v>v<<<<<>^^vv^>>v>^<^<v^v^>^v>>v>^v<><>^<^>v>v<<<^^^v>^<<<>vvv^v^^>^>>^>v>v<>^^><>>v>^>v<<<^^^v^<v^vv>><><^<^<><vvv<v^>>^v>vv<^v<<^vv>v^<<v>v>v>^v^>^v<<^v^vv>v<v>^<<><v^>>v<>><v<<<^v<<>vvv^<vv<vvv<<>^vv^^v><^>v^vv<<v^<<^^^<^<>^^<<>v<><<v>^><>^<><<v<v^^>vv<>^<v<^<vvv>vv>v><^^v<>><^v^v><><>><v<v>vv<>>><v^^v<>><<^>>><^^^vvv<<<vv<<^v<<<>><<vv>>>>v<<<<<vv><><v>v^^<<^vv^<vv<>>vv>^<>^v^^<>^^^vv>v^^<v<><v>v<v>>^v<v<>>^<v^^><>v^^^>v^^v<vv><^>v^v^<>v>v<v<^^>>v<^^vv^v<^^^^vv<<><<^>>^^<<v^^<<^>v^>>^^^><^^>^v^v>^<<v<vv<<<v<^^^>^>>^v<>^<^>v>^>^v^<^^^<^vv<v><^^>>v<v>^>^v^>>>>^v>^^<<^<v^v<^<<v<<^><^^<v^<><v>v^<<v^^<><<>>><vv<<><>^<>>>v<<v^^^v^^<<<vv<<^<^<^vv^<><><<^^<^^>v^>^<v<>>v^v<><<v>^^v>^<^<vvv<v>v^v>>>^^<^<v^>^vv<<<v<<>^><><^<>v>>>v<v^<>v>><^^^v^^^v<^^<vv^^^>v>v<>>^^<><>v>^<v<>^>>>><>v>^v>^vv^v<vv<<^^>><v<>^>^^<v<^>^<vvv>><>^<<>>><<<><>^^<<<v<>v^>v>v<v>^^^>^>^v<<>v>vv>><<<v>^^<v><vv<<v^^>^>>^><^>v<^<^v>><^^>v<vv^^><><>^><<><>v^>v<><^^>><>^<^^v<^<<v>><v><<<^^<<v<^vv^v<>><>>>^>v<vvv^>^<><v^><^<<^vv<^v^v^v<>v^^v>v^<^>^vv^>>><<>v^vv^<>^v^><<v^v<v>v^<><>>v^v^><>v^vvv^^^<<^<<v<<v<^vv^>>v^v>^^<v<>><>v>>v^<>^>v>^>><<>v^v><^v>v>>><v<v><^<^^>vv<v><^>^<^>^^v><><v<^^v<<><^<<v^<v<<><^^vvv^v>^>^<>>vv>v^^v^^vv<^^>><v^^vv><^v>v^<<v<^v>vvv<>>^v><<>^v<<<>^><^vv><<^^<v^>v<<v>^vv<>^v>>>><<<<^^<^v>^<^^<^<^^>>" <> ...

Solution

defmodule Day03 do
  defdelegate parse(input), to: __MODULE__.Input

  @starting_position {0, 0}
  @starting_map %{
    @starting_position => 1
  }
  @starting_map2 %{
    @starting_position => 2
  }

  def part1(input) do
    input
    |> parse()
    |> Enum.reduce(
      {@starting_position, @starting_map},
      &process_delivery/2
    )
    |> elem(1)
    |> map_size()
  end

  def part2(input) do
    input
    |> parse()
    |> Enum.reduce(
      {@starting_position, @starting_position, @starting_map2},
      &process_delivery_part2/2
    )
    |> elem(2)
    |> map_size()
  end

  def process_delivery(direction, {pos, map}) do
    new_pos = move(pos, direction)

    {new_pos, deliver(new_pos, map)}
  end

  def process_delivery_part2(direction, {pos1, pos2, map}) do
    new_pos = move(pos1, direction)

    {pos2, new_pos, deliver(new_pos, map)}
  end

  def move({x, y}, ?^), do: {x, y + 1}
  def move({x, y}, ?>), do: {x + 1, y}
  def move({x, y}, ?v), do: {x, y - 1}
  def move({x, y}, ?<), do: {x - 1, y}
  def deliver(pos, map), do: Map.update(map, pos, 1, &(&1 + 1))

  defmodule Input do
    def parse(input), do: String.to_charlist(input)
  end
end

{:module, Day03, <<70, 79, 82, 49, 0, 0, 14, ...>>,
 {:module, Day03.Input, <<70, 79, 82, ...>>, {:parse, 1}}}

How many houses receive at least one present?

Your puzzle answer was 2572.

Day03.part1(input)

2572

QUESTION TWO?

Your puzzle answer was 2631.

Day03.part2(input)

2631

Both parts of this puzzle are complete! They provide two gold stars: **

At this point, you should return to your Advent calendar and try another puzzle.

If you still want to see it, you can get your puzzle input.

Tests

ExUnit.start(auto_run: false)

defmodule Day03Test do
  use ExUnit.Case, async: false

  describe "part1/1" do
    test "returns expected value" do
      assert Day03.part1(">") == 2
      assert Day03.part1("^>v<") == 4
      assert Day03.part1("^v^v^v^v^v") == 2
    end
  end

  describe "part2/1" do
    test "returns expected value" do
      assert Day03.part2("^v") == 3
      assert Day03.part2("^>v<") == 3
      assert Day03.part2("^v^v^v^v^v") == 11
    end
  end
end

ExUnit.run()

..
Finished in 0.00 seconds (0.00s async, 0.00s sync)
2 tests, 0 failures

Randomized with seed 125335

%{excluded: 0, failures: 0, skipped: 0, total: 2}