Solution to Advent of Code 2022, Day 6.

Day06.elm

module Day06 exposing (partOne, partTwo)

import Set exposing (Set)


type alias Signal =
    String


findStartOfPacketMarker : Int -> Signal -> Int
findStartOfPacketMarker size signal =
    let
        helper : Int -> List Char -> Int
        helper sequenceStart characters =
            let
                sequence : Set Char
                sequence =
                    List.take size characters |> Set.fromList
            in
            if not (Set.size sequence == size) then
                helper (sequenceStart + 1) (List.drop 1 characters)

            else
                sequenceStart + size
    in
    helper 0 (String.toList signal)


partOne : String -> Int
partOne =
    findStartOfPacketMarker 4


partTwo : String -> Int
partTwo =
    findStartOfPacketMarker 14