day01.livemd

Advent of Code 2021 - Day 1

Puzzle description

Sonar Sweep.

The sonar sweep report

defmodule Load do
  def input do
    File.read!("inputs/day01.txt")
    |> String.split("\n", trim: true)
    |> Enum.map(&String.to_integer/1)
  end
end

Figure out how quickly the depth increases

Count the number of times a depth measurement increases from the previous measurement.

defmodule Part1 do
  def scan_depth([_], count) do
    count
  end

  def scan_depth([prev_depth, new_depth | _] = depths, count) do
    count = if new_depth > prev_depth, do: count + 1, else: count
    scan_depth(tl(depths), count)
  end
end

Part1.scan_depth(Load.input(), 0)

Now consider sums of a three-measurement sliding window

Count the number of times the sum of measurements in this sliding window increases from the previous sum.

defmodule Part2 do
  def scan_depth_three(depths) do
    Enum.chunk_every(depths, 3, 1)
    |> Enum.map(&Enum.sum/1)
    |> Part1.scan_depth(0)
  end
end

Part2.scan_depth_three(Load.input())

Check that my answers are still correct after refactoring

ExUnit.start(autorun: false)

defmodule Test do
  use ExUnit.Case, async: true
  @input Load.input()

  test "part1" do
    assert Part1.scan_depth(@input, 0) == 1529
  end

  test "part2" do
    assert Part2.scan_depth_three(@input) == 1567
  end
end

ExUnit.run()