Day 2: Dive!

Intro

https://adventofcode.com/2021/day/2

Read Input - Common for part 1 and 2

input_test =
  """
  forward 5
  down 5
  forward 8
  up 3
  down 8
  forward 2
  """
  |> String.split("\n", trim: true)
  |> Enum.map(fn x -> String.split(x, " ") end)
  |> Enum.map(fn [op, d] -> {op, String.to_integer(d)} end)

input =
  File.read!("input02.txt")
  |> String.split("\n", trim: true)
  |> Enum.map(fn x -> String.split(x, " ") end)
  |> Enum.map(fn [op, d] -> {op, String.to_integer(d)} end)

Part 1 - Testing

Chose to solve this as a map/reduce problem, and accumulate the different values in the reducer

{depth, forward} =
  Enum.reduce(input_test, {0, 0}, fn {operation, distance}, {depth, forward} ->
    case operation do
      "down" -> {depth + distance, forward}
      "up" -> {depth - distance, forward}
      "forward" -> {depth, forward + distance}
    end
  end)

IO.puts("Depth: " <> to_string(depth))
IO.puts("Forward: " <> to_string(forward))
solution = depth * forward

Expected solution should be 150

Part 1 - Running

{depth, forward} =
  Enum.reduce(input, {0, 0}, fn {operation, distance}, {depth, forward} ->
    case operation do
      "down" -> {depth + distance, forward}
      "up" -> {depth - distance, forward}
      "forward" -> {depth, forward + distance}
    end
  end)

IO.puts("Depth: " <> to_string(depth))
IO.puts("Forward: " <> to_string(forward))
solution = depth * forward

Correct answer: 2120749

Part 2 - testing

{depth, forward, aim} =
  Enum.reduce(input_test, {0, 0, 0}, fn {operation, unit}, {depth, forward, aim} ->
    case operation do
      "down" -> {depth, forward, aim + unit}
      "up" -> {depth, forward, aim - unit}
      "forward" -> {depth + aim * unit, forward + unit, aim}
    end
  end)

IO.puts("Depth: " <> to_string(depth))
IO.puts("Forward: " <> to_string(forward))
IO.puts("Aim: " <> to_string(aim))
solution = depth * forward

Correct answer: 900

Part 2 - running

{depth, forward, aim} =
  Enum.reduce(input, {0, 0, 0}, fn {operation, unit}, {depth, forward, aim} ->
    case operation do
      "down" -> {depth, forward, aim + unit}
      "up" -> {depth, forward, aim - unit}
      "forward" -> {depth + aim * unit, forward + unit, aim}
    end
  end)

IO.puts("Depth: " <> to_string(depth))
IO.puts("Forward: " <> to_string(forward))
IO.puts("Aim: " <> to_string(aim))
solution = depth * forward

Correct answer: 2138382217