advent2017-day17.fs

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Problem A
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

type SpinlockState = { position: int; counter: int; list: int list }

let rec insert position value list =
    if position = 0 then value::list
    else
        match list with
        | head::tail -> head::(insert (position-1) value tail)
        | [] -> []

let spinlock spins (state: SpinlockState) =
    let newPosition = (((state.position + spins) % state.list.Length) + 1)
    let newList = insert newPosition state.counter state.list
    { position = newPosition; counter = state.counter + 1; list = newList }
    
let finalState =
    { 1..2017 }
    |> Seq.fold
        (fun s _ -> spinlock 371 s)
        { position = 0; counter = 1; list = [0] }
      
(List.nth finalState.list (finalState.position + 1)).Dump("After 2017")


// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Problem A
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

type SpinlockState2 = { position: int; counter: int; afterZero: int }

let spinlock2 spins state =
    let newPosition = (((state.position + spins) % state.counter) + 1)
    { position = newPosition; counter = state.counter + 1; afterZero = (if newPosition = 1 then state.counter else state.afterZero) }

let finalState2 =
    { 1..50000000 }
    |> Seq.fold
        (fun s _ -> spinlock2 371 s)
        { position = 0; counter = 1; afterZero = 0 }

(finalState2.afterZero).Dump("After zero")