Day07.fs

module Day07

open System

let parse =
    Seq.map (
        splitOn ':'
        >> pair
        >> map2 (int64, allInt64 >> Seq.toList)
    )

let concat a b =
    let p =
        MathF.Log10(float32 b)
        |> fun l -> pown 10L (int l + 1)

    (a * p) + b

let run ops (n, xs) =

    let rec go a =
        function
        | x :: xs' ->
            ops
            |> Seq.tryPick (flip uncurry (a, x) >> flip go xs')
        | [] when a = n -> Some n
        | _ -> None

    match go 0L xs with
    | Some v -> v
    | _ -> 0L

let part1 = Seq.map (run [ (+); (*) ]) >> Seq.sum

let part2 = Seq.map (run [ (+); (*); concat ]) >> Seq.sum

let Solve: string seq -> int64 * int64 = parse >> both part1 part2