path: root/day13.fsx

#r "nuget: astar-search, 1.0.2"
open AStar

let isWall (x, y) =
    let bits = System.Convert.ToString(x*x + 3*x + 2*x*y + y + y*y + 1350, 2)
    bits |> Seq.filter ((=) '1') |> Seq.length |> fun x -> x % 2 = 1

let neighbours (x, y) =
    let found = seq [ (x+1, y); (x, y+1); (x-1, y); (x, y-1) ]
    found |> Seq.filter (fun (nx, ny) -> 
        nx >= 0 && ny >= 0 &&
        not <| isWall(nx, ny))

let gScore _ _ = 1.
let fScore (x, y) (gx, gy) = 
    sqrt ((float gx - float x)**2. + (float gy - float y)**2.)

// part 1
match search (1, 1) (31, 39) {neighbours=neighbours; gCost=gScore; fCost=fScore; maxIterations=None} with
    | Some path -> 
        printfn "%d" <| Seq.length path - 1
    | None -> printfn "0"

// part 2
let mutable count = 0
for i = 0 to 51 do
    for j= 0 to 51 do
        if i+j <= 52 && not (isWall(i, j)) && not (Set.contains (i,j) (Set.ofList [ (0, 51); (0, 52); (51, 0); (52, 0) ])) 
        then
            match search (1, 1) (i, j) {neighbours=neighbours; gCost=gScore; fCost=fScore; maxIterations=None} with
                | Some path -> 
                    if Seq.length path - 1 <= 50 then
                        count <- count + 1
                | None -> ()

printfn "%d" count