Walking along the memory banks of the stream, you find a small village that is experiencing a little confusion: some programs can't communicate with each other.

Programs in this village communicate using a fixed system of pipes. Messages are passed between programs using these pipes, but most programs aren't connected to each other directly. Instead, programs pass messages between each other until the message reaches the intended recipient.

Read the full puzzle.

using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace AdventOfCode.Y2017.Day12;

class Node {
    public string Id;
    public List<string> Neighbours;
}

[ProblemName("Digital Plumber")]
class Solution : Solver {

    public object PartOne(string input) => GetPartitions(input).Single(x => x.Contains("0")).Count();
    public object PartTwo(string input) => GetPartitions(input).Count();

    IEnumerable<HashSet<string>> GetPartitions(string input) {
        var nodes = Parse(input);
        var parent = new Dictionary<string, string>();

        string getRoot(string id) {
            var root = id;
            while (parent.ContainsKey(root)) {
                root = parent[root];
            }
            return root;
        }

        foreach (var nodeA in nodes) {
            var rootA = getRoot(nodeA.Id);
            foreach (var nodeB in nodeA.Neighbours) {
                var rootB = getRoot(nodeB);
                if (rootB != rootA) {
                    parent[rootB] = rootA;
                }
            }
        }

        return
            from node in nodes
            let root = getRoot(node.Id)
            group node.Id by root into partitions
            select new HashSet<string>(partitions.ToArray());
        
    }

    List<Node> Parse(string input) {
        return (
            from line in input.Split('\n')
            let parts = Regex.Split(line, " <-> ")
            select new Node() {
                    Id = parts[0],
                    Neighbours = new List<string>(Regex.Split(parts[1], ", "))
                }
        ).ToList();
    }

}

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