Elixir

Oh wow I’m late but that’s because I decided to do this year in Elixir which I am not really experienced enough yet as it seems. Part 1 was ok but I didn’t really put enough thought into Part 2 and got stuck for a while. However I got it done after a few failed tries and a few questions to AI on how to do things in Elixir.

#!/usr/bin/elixir

defmodule SafeDial do

def readInstructions(filename) do
	filename
	|> File.stream!()
	|> Stream.map(&String.trim/1)
	|> Stream.reject(&(&1 == ""))
	|> Stream.map(fn line ->
		case Regex.run(~r/^([A-Za-z])(\d+)$/, line) do
			[_, letter, number] -> {String.to_atom(letter), String.to_integer(number)}
			_ -> nil
		end
	end)
	|> Enum.reject(&(&1 == nil))
end

def evalInstructions(instructions) do
	initialPos = 50
	zeroCount = 0
	checkInstruction(instructions, initialPos, zeroCount)
end

defp checkInstruction(instructions, currPos, zeroCount) do
	case instructions do
		[] -> {currPos, zeroCount}
		[instruct | rest] ->
			nextPos =
				case instruct do
					{dir, step} when dir == :R and currPos + rem(step,100) > 99 ->
						currPos + rem(step,100) - 100
					{dir, step} when dir == :R and currPos + rem(step,100) > 99 ->
						currPos + rem(step,100) - 100
					{dir, step} when dir == :R ->
						currPos + rem(step,100)
					{dir, step} when dir == :L and currPos - rem(step,100) < 0 ->
						currPos - rem(step,100) + 100
					{dir, step} when dir == :L ->
						currPos - rem(step,100)
					_ -> raise "[ ERROR ] unkown instruction: #{inspect(instruct)}"
				end
			newZeroCount = if nextPos == 0, do: zeroCount + 1, else: zeroCount
			checkInstruction(rest, nextPos, newZeroCount)
		other -> raise "[ ERROR ] unknown instruction: #{inspect(other)}"
	end
end

def evalInstructionsPart2(instructions) do
	initialPos = 50
	zeroCount = 0
	checkInstructionPart2(instructions, initialPos, zeroCount)
end

defp checkInstructionPart2(instructions, currPos, zeroCount) do
	case instructions do
		[] -> {currPos, zeroCount}
		[instruct | rest] ->
			{nextPos, zeroCount1} =
				case instruct do
					{dir, step} when dir == :R and currPos + rem(step,100) == 100 ->
						{currPos + rem(step,100) - 100, zeroCount+floor(step/100)}
					{dir, step} when dir == :R and currPos + rem(step,100) > 99 ->
						{currPos + rem(step,100) - 100, zeroCount+floor(step/100)+1}
					{dir, step} when dir == :R ->
						{currPos + rem(step,100), zeroCount+floor(step/100)}
					{dir, step} when dir == :L and currPos == 0 and currPos - rem(step,100) < 0 ->
						{currPos - rem(step,100) + 100, zeroCount+floor(step/100)}
					{dir, step} when dir == :L and currPos - rem(step,100) < 0 ->
						{currPos - rem(step,100) + 100, zeroCount+floor(step/100)+1}
					{dir, step} when dir == :L ->
						{currPos - rem(step,100), zeroCount+floor(step/100)}
					_ -> raise "[ ERROR ] unkown instruction: #{inspect(instruct)}"
				end
			newZeroCount = if nextPos == 0, do: zeroCount1 + 1, else: zeroCount1
			checkInstructionPart2(rest, nextPos, newZeroCount)
		other -> raise "[ ERROR ] unknown instruction: #{inspect(other)}"
	end
end

end #module

IO.puts "### PART 1 ###"
instructions = SafeDial.readInstructions("input/day01Input.txt")
{finalPos, zeroCount} = SafeDial.evalInstructions(instructions)
IO.puts "final position:#{finalPos} zero count:#{zeroCount}"

IO.puts "### PART 2 ###"
instructions = SafeDial.readInstructions("input/day01Input.txt")
{finalPos, zeroCount} = SafeDial.evalInstructionsPart2(instructions)
IO.puts "final position:#{finalPos} zero count:#{zeroCount}"

Edit: removed debug output