path: root/day12.fsx

open System.IO
open System.Text.RegularExpressions
open System.Collections.Generic

let getConnection line = 
    let idRegex = new Regex("\d+")
    let ids = idRegex.Matches(line)
    match [for ID in ids -> ID.Value] with
    | [] -> ("", [])
    | head::tail -> (head, tail)

let rec visit (connections: Dictionary<string, list<string>>) (visited: HashSet<string>) origin =
    if not (visited.Add(origin)) then ()
    else
        for child in connections[origin] do visit connections visited child

let checkInGroups (groups: seq<HashSet<string>>) (origin:string) =
    Seq.fold (fun acc (group: HashSet<string>) -> acc || group.Contains(origin)) false groups

let () = 
    let pipes = new Dictionary<string, list<string>>()
    File.ReadAllLines "day12.txt" |> Array.map getConnection |> Array.iter (fun (head, tail) -> pipes[head] <- tail)

    let reachable = new HashSet<string>()
    visit pipes reachable "0"
    printfn "%A" reachable.Count
    
    let groups = new List<HashSet<string>>()
    for origin in pipes.Keys do
        if checkInGroups groups origin then ()
        else
            let newGroup = new HashSet<string>()
            visit pipes newGroup origin
            groups.Add(newGroup)
        
    printfn "%A" groups.Count