day15.fsx

let readLines filePath = System.IO.File.ReadLines(filePath);;

let input = readLines "day15.txt" |> List.ofSeq

let parse (txt: string) =
 let b = txt.Split(": closest beacon is at x=")
 let xy = b[0].Split(", y=")
 let x = xy[0].Substring("Sensor at x=".Length)
 let y = xy[1]
 let bxy = b[1].Split(", y=")
 let bx = bxy[0]
 let by = bxy[1]
 (int x, int y), (int bx, int by)

let sbs = input |> List.map parse

let dist (x1: int, y1: int) (x2, y2)= abs (x1 - x2) + abs (y1 - y2)

let ds = List.map (fun (a, b) -> dist a b) sbs

let beacons = sbs |> List.map snd

let minX = sbs |> List.collect (fun (x, y) -> [fst x; fst y]) |> List.min |> (fun x -> (-) x (List.max ds))
let maxX = sbs |> List.collect (fun (x, y) -> [fst x; fst y]) |> List.max |> (+) (List.max ds)

let dsb = List.zip ds (List.map fst sbs)

let inRangeOfABeacon (x: int, y: int) =
 List.fold (fun s (a, b) -> s || (dist (x,y) b) <= a ) false dsb

let inRangeButNotBeacon (x,y) =
 inRangeOfABeacon (x,y) && beacons |> List.contains (x,y) |> not

let y = 2000000
[minX .. maxX]
|> List.map (fun x -> (x, y))
|> List.map inRangeButNotBeacon
|> List.filter id
|> List.length
|> printf "Day 15 (1): %A\n"

let tuningFrequency (x,y) = int64 x * int64 4000000 + int64 y

let inRange (x,y) = x >= 0 && x <= 4000000 && y >= 0 && y <= 4000000

let border (x,y) d = 
 let l = x - d - 1
 let r = x + d + 1
 let u = y - d - 1
 let d = y + d + 1
 let s1 = List.zip [x .. r] [y .. d]
 let s2 = List.zip [x .. r] [u .. y]
 let s3 = List.zip [l .. x] [y .. d]
 let s4 = List.zip [l .. x] [u .. y]
 (s1 @ s2 @ s3 @ s4) |> List.filter inRange

dsb
|> List.map (fun (d, (x,y)) -> border (x,y) d)
|> List.collect (List.filter (inRangeOfABeacon >> not))
|> List.head
|> tuningFrequency
|> printf "Day 15 (2): %A\n"