Advent of code 2025 day 1

Mix.install([
  {:kino, "~> 0.18"}
])

Part 1

https://adventofcode.com/2025/day/1

input = Kino.Input.textarea("Please give me input:")

rotations =
  Kino.Input.read(input)
  |> String.split("\n", trim: true)
  |> Enum.map(fn
    "L" <> rotate -> {-1, String.to_integer(rotate)}
    "R" <> rotate -> {1, String.to_integer(rotate)}
  end)

length(rotations)

Enum.reduce(rotations, {0, 50}, fn {sign, rotate}, {null_count, dail_position} ->
  new_position = dail_position + sign * Integer.mod(rotate, 100)
  new_position = if new_position < 0, do: new_position + 100, else: Integer.mod(new_position, 100)
  new_null_count = if new_position == 0, do: null_count + 1, else: null_count
  {new_null_count, new_position}
end)

# prints {null count, last position}

Part 2

Enum.reduce(rotations, {0, 50}, fn {sign, rotate}, {null_count, dail_position} ->
  new_position = dail_position + sign * Integer.mod(rotate, 100)
  extra_counts = div(rotate, 100)
  new_null_count = if (new_position <= 0 and dail_position != 0) or new_position >= 100, do: null_count + 1, else: null_count
  new_position = if new_position < 0, do: new_position + 100, else: Integer.mod(new_position, 100)
  {new_null_count + extra_counts, new_position}
end)

# prints {null count, last position}