AdventOfCode_Day11.fsx

open System
open System.Text

let getCharEx (input : int) =
    Encoding.ASCII.GetString([| byte (97 + (int (input % 26))) |]).ToCharArray().[0]

let codeToChar =
    seq { for i = 0 to 25 do yield (uint64 i), getCharEx i }
    |> dict

let charToCode =
    seq { for i = 0 to 25 do yield getCharEx i, (uint64 i) }
    |> dict

let getCode (input : char) = charToCode.[input]

let getChar (input : uint64)  = codeToChar.[input]

let convertToInt (input : string) =
    let rec convertToIntLoop (acc : uint64) (part : char list) =
        match part with
        | [] -> acc
        | head :: tail -> convertToIntLoop ((acc * 26UL) + (getCode head)) tail
    convertToIntLoop 0UL (input.ToCharArray() |> Array.toList)

let convertToString (input : uint64) =
    let rec convertToStringLoop (acc : char list) (i : uint64) =
        if i = 0UL then acc
        else convertToStringLoop ((getChar (i % 26UL)) :: acc) (uint64 (Math.Floor (float (i / 26UL))))
    convertToStringLoop List.empty input
    |> List.toArray
    |> (fun x -> (new String(x)).PadLeft(8, 'a'))

let hasTwoPer (input : string) =
    input.ToCharArray()
    |> Seq.pairwise
    |> Seq.filter (fun (a, b) -> a = b)
    |> Seq.map (fun (a, b) -> a)
    |> Seq.distinct
    |> Seq.length
    |> (fun x -> x >= 2)

let hasRestricted (input : string) =
    input.ToCharArray()
    |> Seq.exists (fun x -> x = 'i' || x = 'o' || x = 'l')

let hasConsecutive (input : string) =
    let s = input.ToCharArray()
    seq {
        for i = 0 to s.Length - 3 do
            yield (s.[i], s.[i+1], s.[i+2])
    }
    |> Seq.exists (fun (a, b, c) -> (getCode b) = ((getCode a) + 1UL) && (getCode c) = ((getCode b) + 1UL))

let isValidPassword (input : string) =
    (hasTwoPer input) && (not (hasRestricted input)) && (hasConsecutive input)

let findNextPassword (input : string) =
    let asInt = convertToInt input
    seq { for x = (asInt + 1UL) to UInt64.MaxValue do yield convertToString x }
    |> Seq.find isValidPassword

let part1 = findNextPassword "hepxcrrq"
let part2 = findNextPassword part1