AdventOfCode2022 December 6

AdventOfCode2022.12.06.fsx

open System
open System.IO

let input =
    File.ReadAllLines(__SOURCE_DIRECTORY__ + "input06.txt")
    |> Seq.head
    |> Seq.toArray

// First solution uses "windowed" function. It is not memory efficient because it allocates large number of arrays
// (the number of allocated arrays is approximately the count of characters in input string)

let getResult distinctLength  =
    input 
    |> Array.windowed distinctLength
    |> Array.findIndex (fun range -> range |> Array.distinct |> Array.length = distinctLength)
    |> (+) distinctLength

// Part One
getResult 4

// Part Two
getResult 14

// Second solution uses recursive function and does not suffer from excessive memory allocation

let rec getResult chars ndx distinctLength  =
    if chars |> Array.truncate distinctLength |> Array.distinct |> Array.length = distinctLength
    then ndx + distinctLength
    else getResult (chars |> Array.skip 1) (ndx+1) distinctLength

// Part One
getResult input 0 4

// Part Two
getResult input 0 14