day9.fsx


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open System.IO
open System.Text.RegularExpressions

let (|Regex|_|) input =
    let m = Regex.Match(input, "^(?:\((\w+?)\))(.*)")
    if m.Success then Some(List.tail [for g in m.Groups -> g.Value])
    else None

let splitPattern str =
    match str with 
    | Regex [marker; rest] -> marker, rest
    | _ -> "", ""

let rec decrypt str =
    if str = "" then ""
    else
        let marker, rest = splitPattern str
        if marker = "" then string str[0] + decrypt str[1..]
        else
            let nums = marker.Split 'x' |> Array.map int
            let start, count = (min nums[0] (String.length rest)), nums[1]
            String.replicate count rest[..start-1] + decrypt rest[start..]

let rec decryptLength str =
    if str = "" then bigint 0
    else
        let marker, rest = splitPattern str
        if marker = "" then bigint 1 + decryptLength str[1..]
        else
            let nums = marker.Split 'x' |> Array.map int
            let start, count = (min nums[0] (String.length rest)), nums[1]
            bigint count * decryptLength rest[..start-1] + decryptLength rest[start..]

let lines = File.ReadLines "day9.txt"
lines |> Seq.map decrypt |> Seq.map String.length |> Seq.reduce (+) |> printfn "%d"
lines |> Seq.map decryptLength |> Seq.reduce (+) |> printfn "%A"