coding-challenges/everybody-codes/2025/EveryBodyCodes2025/EveryBodyCodes_WrongOne/QuestOne.fs

module EveryBodyCodes2025.QuestOne

open System
open System.Collections.Generic
open System.IO
open System.Linq
open System.Numerics
open System.Threading.Tasks

let eni (n:BigInteger) (exp:BigInteger) (m:BigInteger) =
    let mutable remainders = []
    let mutable score = BigInteger 1 
    for _ in (BigInteger 1)..exp do
        score <- (score * n) % m
        remainders <- score::remainders
    List.rev remainders  // Reverse to get correct order (oldest first)
        
// let test1 = eni 2 4 5 |> fun l -> String.Join("", l) |> int64
// let test2 = eni 3 5 16 |> fun l -> String.Join("", l) |> int64

let part1Lines (input:String array) =
    input |> Array.map (fun line ->
        line.Split(" ") |> Array.map(fun segment ->
            let parts = segment.Split("=")
            let alias = parts[0]
            let num = parts[1] |> BigInteger.Parse
            (alias, num)
            )
        |> dict
    )
    
let toBigInt (list:'a list) = String.Join("", list) |> BigInteger.Parse
    
let part1 (input: IDictionary<string, BigInteger> array)=
    input
    |> Seq.map (fun line ->
        let a = eni line["A"] line["X"] line["M"] |> toBigInt
        let b = eni line["B"] line["Y"] line["M"] |> toBigInt
        let c = eni line["C"] line["Z"] line["M"] |> toBigInt
        a + b + c
    ) |> Seq.max
    |> fun x ->
        printfn $"{x}"
        x
    
let part1Answer =
    File.ReadAllLines "Inputs/Q01_P01.txt"
    |> part1Lines
    |> part1
    
/// Map from (prev, curr) pair to position
type PositionMap = Map<BigInteger * BigInteger, BigInteger * BigInteger>
let rec findCycle (pairToNextPair: PositionMap) startPair currentPair acc =
    if currentPair = startPair && List.length acc > 0 then
        Some (List.rev acc)
    else
        match Map.tryFind currentPair pairToNextPair with
        | None -> None
        | Some nextPair -> 
            findCycle pairToNextPair startPair nextPair (snd currentPair :: acc)

let rec eni2' score (n:BigInteger) (exp:BigInteger) (m:BigInteger) (pairMap: PositionMap) (scores:BigInteger list) iter =
    if iter > exp then scores |> List.rev |> List.skip (max 0 (List.length scores - 5)) |> toBigInt
    else
        let newScore = (score * n) % m
        let key = (score, newScore)
        
        match Map.tryFind key pairMap with
        | Some _ -> 
            match findCycle pairMap key key [] with
            | Some cycle ->
                let remaining = int64 (exp - iter)
                let cycleValues = cycle
                let cycleLength = List.length cycleValues |> int64
                let scoresLength = List.length scores |> int64
                let totalLength = scoresLength + 1L + remaining // scores + newScore + remaining
                
                let needCount = min 5L totalLength
                let startPos = max 0L (totalLength - needCount)
                
                let scoresReversed = List.rev scores
                
                let final5 = 
                    [startPos..totalLength - 1L]
                    |> List.map (fun pos ->
                        if pos < scoresLength then
                            // Position is in scores (scores is reversed, so oldest is at end)
                            scoresReversed.[int pos]
                        elif pos = scoresLength then
                            // Position is newScore
                            newScore
                        else
                            let cycleOffset = pos - scoresLength
                            let cyclePos = cycleOffset % cycleLength
                            cycleValues.[int cyclePos]
                    )
                
                // final 5 comes out in reverse order
                final5 |> List.rev |> toBigInt
            | None -> 
                eni2' newScore n exp m (Map.add key ((newScore, (newScore * n) % m)) pairMap) (newScore::scores) (iter + BigInteger 1)
        | None ->
            let nextPair = (newScore, (newScore * n) % m)
            eni2' newScore n exp m (Map.add key nextPair pairMap) (newScore::scores) (iter +  BigInteger 1)

let eni2 (n) (exp) (m) = eni2' (BigInteger 1) n exp m Map.empty [] (BigInteger 1)

let part2 (input: IDictionary<string, BigInteger> array)=
    input
    |> Array.mapi (fun i line ->
        //printfn $"""running line {line.AsEnumerable() |> Seq.map(fun kv -> kv.Key + "=" + kv.Value.ToString()) |> fun x -> String.Join(", ", x)}"""
        let a = eni2 line["A"] line["X"] line["M"]
        let b = eni2 line["B"] line["Y"] line["M"]
        let c = eni2 line["C"] line["Z"] line["M"]
        let ret = a + b + c
        //printfn $"found {ret}"
        ret
    ) |> Seq.max
    
let test2 =
    let a = eni2 5 6 15
    let b = eni2 9 16 15
    let c = eni2 7 18 15
    let r = a + b + c
    printfn $"{r}"
    r
    

let part2Answer = 
    File.ReadAllLines "Inputs/Q01_P02.txt"
    |> part1Lines
    |> part2
    |> fun x ->
        printfn $"part2 {x}"
        x
        
let part2Answer' file =
     File.ReadAllLines file
    |> part1Lines
    |> part2
    |> fun x ->
        printfn $"part2 {x}"
        x