advent2017-day19.fs

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Input data
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

let parse filename =
    File.ReadAllLines(filename)
    |> Seq.map (fun line -> line |> Array.ofSeq)
    |> Array.ofSeq

let data = parse "queries/Advent/Advent2017-day19.txt"

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Problem A + B
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

let getMapCell map x y =
    if (y < 0 || y >= Array.length map) then None
    else
        let row = map.[y]
        if (x < 0 || x >= Array.length row) then None
        else Some row.[x]

let traverse map =
    let getMapCell' = getMapCell map
    let rec traverse' (x,y) (dx,dy) (message: char list) steps =
        let cell = getMapCell' x y
        match cell with
        | None -> (message,steps)
        | Some cellValue ->
            match cellValue with
            | '|' -> traverse' (x+dx,y+dy) (dx,dy) message (steps+1)
            | '-' -> traverse' (x+dx,y+dy) (dx,dy) message (steps+1)
            | '+' when dx <> 0 ->
                let dy' =
                    match (getMapCell' x (y-1)) with
                    | None -> 1
                    | Some ' ' -> 1
                    | _ -> -1
                traverse' (x,y+dy') (0,dy') message (steps+1)
            | '+' when dy <> 0 ->
                let dx' =
                    match (getMapCell' (x-1) y) with
                    | None -> 1
                    | Some ' ' -> 1
                    | _ -> -1
                traverse' (x+dx',y) (dx',0) message (steps+1)
            | letter when letter >= 'A' && letter <= 'Z' -> traverse' (x+dx,y+dy) (dx,dy) (letter::message) (steps+1)
            | ' ' -> (message,steps)
            | _ -> raise (InvalidOperationException ("Unknown cell \"" + (string cellValue) + "\""))
        
    let startPositionX = data.[0] |> Array.findIndex ((=) '|')
    traverse' (startPositionX,0) (0,1) [] 0

let (message,steps) = traverse data
(message |> List.rev |> Seq.ofList |> Seq.map string |> String.concat "").Dump("Message")
steps.Dump("Steps")