Advent of Code 2020 day 22 in F#

aoc2020day22.fsx

#time "on"

let txt = System.IO.File.ReadAllText( __SOURCE_DIRECTORY__ + "/input.txt").Trim()

let player1, player2 = 
    let m = txt.Split("\n\n") |> Array.map(fun s -> s.Split("\n") |> Array.tail |> Array.map int |> Array.toList)
    m.[0], m.[1] 

let pressPlay1 () = 
    let rec play p1 p2 =
        match p1, p2 with
        | [], p -> p
        | p, [] -> p
        | h1::t1, h2::t2 ->
            let t1', t2' =
                if h1 > h2 then 
                    t1 @ [h1; h2], t2
                else
                    t1, t2 @ [h2;h1]
            play t1' t2'
    play player1 player2

let pressPlay2 () = 
    let isnewmatch h1 t1 h2 t2 =
        h1 <= List.length t1 && h2 <= List.length t2

    let rec play rounds g p1 p2  =
        let rounds' = rounds |> Set.add (p1, p2)
        let r = rounds' |> Set.count
        //printfn "-- Round %d (Game %d) --" r g
        //printfn "Player1's deck: %A" p1
        //printfn "Player2's deck: %A" p2
        match p1, p2 with
        | p, [] -> 
            //printfn "Player1 wins round %d of game %d" r g
            p, []
        | [], p -> 
            //printfn "Player2 wins round %d of game %d" r g
            [], p
        | _ when rounds |> Set.contains (p1, p2) ->
            //printfn "SAME ROUND DETECTED: The winner of game %d is player 1!" g
            [0xFFFFFFFF], []
        | h1::t1, h2::t2 when isnewmatch h1 t1 h2 t2 ->
            //printfn "Player1 plays: %A" h1
            //printfn "Player2 plays: %A" h2
            //printfn "Playing a sub-game to determine the winner..."
            let t1' = t1 |> List.take h1
            let t2' = t2 |> List.take h2
            let g' = g + 1
            let t1'', t2'' =
                match play Set.empty g' t1' t2' with
                | p, [] ->
                    //printfn "The winner of game %d is player 1!" g
                    t1 @ [h1; h2], t2
                | [], p ->
                    //printfn "The winner of game %d is player 2!" g
                    t1, t2 @ [h2;h1]
            play rounds' g t1'' t2''
        | h1::t1, h2::t2 ->
            //printfn "Player1 plays: %A" h1
            //printfn "Player2 plays: %A" h2
            let t1', t2' =
                if h1 > h2 then
                    //printfn "Player 1 wins round %d of game %d!" r g
                    t1 @ [h1; h2], t2
                else
                    //printfn "Player 2 wins round %d of game %d!" r g
                    t1, t2 @ [h2;h1]
            play rounds' g t1' t2'
    play Set.empty 1 player1 player2 |> fun (a, b) -> max a b

let countHand hand = hand |> List.rev |> List.mapi(fun i c -> (i + 1) * c) |> List.sum

pressPlay1() |> countHand |> printfn "part 1: %d"
pressPlay2() |> countHand |> printfn "part 2: %d"
// Real: 00:00:11.261, CPU: 00:00:11.513, GC gen0: 758, gen1: 86, gen2: 1