Fsharp

type Day13(lines: string[]) =
    let lines =
        String.Join("", lines)
        |> split2Int64ByReg @"(\d+)"
        |> Array.concat
        |> fun nums -> nums |> Array.splitInto (nums.Length / 6)

    let getMinCost (ai, aj) (bi, bj) (ti, tj) =
        // a * ai + b * bi = ti
        // a * aj + b * bj = tj
        // solve a, b
        // because for every a, b, t only have one or zero int solution
        let d = ai * bj - aj * bi
        let a = (ti * bj - tj * bi) / d
        let b = (tj * ai - ti * aj) / d

        if a * ai + b * bi = ti && a * aj + b * bj = tj then
            Some(a * 3L + b)
        else
            None

    member this.Q1() =
        lines
        |> Array.toList
        |> List.choose (fun nums -> getMinCost (nums[0], nums[1]) (nums[2], nums[3]) (nums[4], nums[5]))
        |> List.sum

    member this.Q2() =
        lines
        |> Array.toList
        |> List.choose (fun nums ->
            getMinCost (nums[0], nums[1]) (nums[2], nums[3]) (10000000000000L + nums[4], 10000000000000L + nums[5]))
        |> List.sum

type Day9(lines: string[]) =
    member this.Q1() =
        let transform (l: string) =
            l
            |> Seq.mapi (fun i c ->
                let n = char2Int c

                if i % 2 = 0 then
                    Array.init n (fun _ -> $"{i / 2}")
                else
                    Array.init n (fun _ -> "."))
            |> Seq.concat
            |> Seq.toArray

        let lines = String.Join("", lines) |> transform

        let rec shift i j =
            if i < j then
                match lines[i] = ".", lines[j] <> "." with
                | true, true ->
                    lines[i] <- lines[j]
                    lines[j] <- "."
                    shift (i + 1) (j - 1)
                | true, false -> shift i (j - 1)
                | false, true -> shift (i + 1) j
                | false, false -> shift (i + 1) (j - 1)

        shift 0 (lines.Length - 1)

        lines
        |> Array.mapi (fun i c -> if c <> "." then int64 i * (int64 c) else 0L)
        |> Array.sum

    member this.Q2() =
        let transform (l: string) =
            l
            |> Seq.mapi (fun i c ->
                let n = char2Int c

                if i % 2 = 0 then
                    Array.init n (fun idx -> (idx + 1, $"{i / 2}"))
                else
                    Array.init n (fun idx -> (n - idx, ".")))
            |> Seq.concat
            |> Seq.toArray

        let lines = String.Join("", lines) |> transform

        let rec shift i j =
            let ni, ci = lines[i]
            let nj, cj = lines[j]

            if i < j then
                match ci = ".", cj <> ".", ni >= nj with
                | true, true, true ->
                    for n in 0 .. nj - 1 do
                        lines[i + nj - n - 1] <- lines[j - n]
                        lines[j - n] <- (fst lines[j - n], ".")

                    shift 0 (j - nj)
                | true, true, false -> shift (i + ni) j
                | false, true, _ -> shift (i + 1) j
                | true, false, _ -> shift i (j - 1)
                | false, false, _ -> shift (i + 1) (j - 1)
            elif cj <> "." && j - nj > 0 then
                shift 0 (j - nj)

        shift 0 (lines.Length - 1)

        lines
        |> Array.mapi (fun i (_, c) -> if c <> "." then int64 i * (int64 c) else 0L)
        |> Array.sum

type Day8(lines: string[]) =
    let R = lines.Length
    let C = lines[0].Length

    let getPoints (lines: string[]) : Map<char, Index array> =
        let points =
            [| for i in 0 .. R - 1 do
                   for j in 0 .. C - 1 do
                       if lines[i][j] <> '.' then
                           (lines[i][j], (i, j)) |]

        points
        |> Array.groupBy fst
        |> Map.ofArray
        |> Map.map (fun _ v -> v |> Array.map snd)


    let inBoard (i, j) : bool = 0 <= i && i < R && 0 <= j && j < C

    let getIdxPair (idx_list: Index array) =
        [ for i in 0 .. idx_list.Length - 2 do
              for j in i + 1 .. idx_list.Length - 1 do
                  (idx_list[i], idx_list[j]) ]

    let getAntinodes op (a: Index) (b: Index) : Index list =
        let ar, ac = a
        let br, bc = b

        let x = abs (ar - br)
        let y = abs (ac - bc)

        match ar < br, ac < bc with
        | true, true -> (-x, -y), (x, y)
        | true, false -> (-x, y), (x, -y)
        | false, true -> (x, -y), (-x, y)
        | false, false -> (x, y), (-x, -y)
        |> fun (d1, d2) -> op a d1 @ op b d2

    member this.Q1() =
        let points_dict = lines |> getPoints
        let getAntIdx (ar, ac) (dr, dc) = [ (ar + dr, ac + dc) ]

        points_dict.Values
        |> Array.ofSeq
        |> Seq.collect (fun idx_list ->
            idx_list
            |> getIdxPair
            |> List.collect (fun (l, r) -> getAntinodes getAntIdx l r))
        |> Seq.filter inBoard
        |> Set.ofSeq
        |> Seq.length

    member this.Q2() =
        let points_dict = lines |> getPoints

        let getAntinodesInLine (ar, ac) (x, y) =
            let rec loop (ar, ac) x y rst =
                if not (inBoard (ar, ac)) then
                    rst
                else
                    loop (ar + x, ac + y) x y ((ar, ac) :: rst)

            loop (ar, ac) x y []

        points_dict.Values
        |> Array.ofSeq
        |> Seq.collect (fun idx_list ->
            idx_list
            |> getIdxPair
            |> List.collect (fun (l, r) -> getAntinodes getAntinodesInLine l r))
        |> Set.ofSeq
        |> Seq.length

type Day6(lines: string[]) =
    let R = lines.Length
    let C = lines[0].Length

    let getStart (lines: string[]) =
        lines
        |> Array.indexed
        // |> Array.pick (fun (i, s) -> s |> Seq.tryFindIndex ((=) '^') |> Option.map (fun j -> (i, j)))
        |> Array.pick (fun (i, s) ->
            let j = s.IndexOf("^")
            if j <> -1 then Some(i, j) else None)

    let ops = [ (-1, 0); (0, 1); (1, 0); (0, -1) ]

    let rec moving i j op (pos_set: HashSet<Index>) =
        pos_set.Add((i, j)) |> ignore
        let next_i = i + fst ops[op]
        let next_j = j + snd ops[op]

        if next_i < 0 || next_i >= R || next_j < 0 || next_j >= C then
            pos_set
        elif lines[next_i][next_j] = '#' then
            moving i j ((op + 1) % 4) pos_set
        else
            moving next_i next_j op pos_set


    member this.Q1() =
        let start: Index = getStart lines
        let post_set = moving (fst start) (snd start) 0 (HashSet())
        post_set.Count

    member this.Q2() =
        let start: Index = getStart lines
        let pos_set = moving (fst start) (snd start) 0 (HashSet())
        pos_set.Remove(start) |> ignore
        let isInLoop (pos_set: HashSet<int * int * int>) i j op = pos_set.Add((i, j, op)) = false

        let rec checkLoop i j op (pos_set: HashSet<int * int * int>) =

            let next_i = i + fst ops[op]
            let next_j = j + snd ops[op]

            if next_i < 0 || next_i >= R || next_j < 0 || next_j >= C then
                false
            elif lines[next_i][next_j] = '#' then
                if isInLoop pos_set i j op then
                    true
                else
                    checkLoop i j ((op + 1) % 4) pos_set
            else
                checkLoop next_i next_j op pos_set


        pos_set
        |> Seq.filter (fun (i, j) ->
            let old = lines[i]
            let str = old.ToCharArray()
            str[j] <- '#'
            lines[i] <- String(str)
            let rst = checkLoop (fst start) (snd start) 0 (HashSet())
            lines[i] <- old
            rst)
        |> Seq.length

module Day3 =
    let Q1 (lines: string[]) =
        let str = String.Concat(lines)
        str |> split2IntByReg "mul\((\d+),(\d+)\)" |> Array.sumBy (fun n -> n[0] * n[1])

    let Q2 (lines: string[]) =
        let str = String.Concat(lines)

        Regex.Matches(str, @"mul\((\d+),(\d+)\)|don't\(\)|do\(\)")
        |> Seq.fold
            (fun (l, isEnable) m ->
                if m.Value.StartsWith("mul") then
                    if isEnable then
                        l @ [ (int m.Groups[1].Value, int m.Groups[2].Value) ], isEnable
                    else
                        l, isEnable
                elif m.Value = "do()" then
                    l, true
                elif m.Value = "don't()" then
                    l, false
                else
                    failwith $"wrong patten m={m.Value}")
            ([], true)
        |> fst
        |> Seq.sumBy (fun (l, r) -> l * r)