The CPU itself is a large, black building surrounded by a bottomless pit. Enormous metal tubes extend outward from the side of the building at regular intervals and descend down into the void. There's no way to cross, but you need to get inside.

No way, of course, other than building a bridge out of the magnetic components strewn about nearby.

Read the full puzzle.

using System;
using System.Collections.Generic;
using System.Linq;

namespace AdventOfCode.Y2017.Day24;

[ProblemName("Electromagnetic Moat")]
class Solution : Solver {

    public object PartOne(string input) => StrongestBridge(input, (a, b) => a.strength - b.strength);
    public object PartTwo(string input) => StrongestBridge(input, (a, b) => a.CompareTo(b));

    int StrongestBridge(string input, Func<(int length, int strength), (int length, int strength), int> compare) {

        (int length, int strength) fold(int pinIn, HashSet<Component> components) {
            var strongest = (0, 0);
            foreach (var component in components.ToList()) {
                var pinOut =
                    pinIn == component.pinA ? component.pinB :
                    pinIn == component.pinB ? component.pinA :
                     -1;

                if (pinOut != -1) {
                    components.Remove(component);
                    var curr = fold(pinOut, components);
                    (curr.length, curr.strength) = (curr.length + 1, curr.strength + component.pinA + component.pinB);
                    strongest = compare(curr, strongest) > 0 ? curr : strongest;
                    components.Add(component);
                }
            }
            return strongest;
        }
        return fold(0, Parse(input)).strength;
    }

    HashSet<Component> Parse(string input) {
        var components = new HashSet<Component>();
        foreach (var line in input.Split('\n')) {
            var parts = line.Split('/');
            components.Add(new Component { pinA = int.Parse(parts[0]), pinB = int.Parse(parts[1]) });
        }
        return components;
    }
}

class Component {
    public int pinA;
    public int pinB;
}

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