You should have been watching where you were going, because as you wander the new North Pole base, you trip and fall into a very deep hole!

Just kidding. You're falling through time again.

Read the full puzzle.

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

namespace AdventOfCode.Y2018.Day21;

[ProblemName("Chronal Conversion")]
class Solution : Solver {

    public object PartOne(string input) => Run(input).First();
    public object PartTwo(string input) => Run(input).Last();

    public IEnumerable<long> Run(string input) {
        var breakpoint = 28;
        var seen = new List<long>();

        foreach (var regs in Trace(input, breakpoint)) {
            if (seen.Contains(regs[3])) {
                break;
            }
            seen.Add(regs[3]);
            yield return regs[3];
        }
    }

    public IEnumerable<long[]> Trace(string input, int breakpoint) {
        var lines = input.Split("\n");
        var ipReg = int.Parse(lines.First().Split(" ")[1]);
        var program = lines.Skip(1).Select(Compile).ToArray();
        var regs = new long[] { 0, 0, 0, 0, 0, 0 };

        while (true) {
            if (regs[ipReg] == breakpoint) {
                yield return regs;
            }
            program[regs[ipReg]](regs);
            regs[ipReg]++;
        }
    }

    Action<long[]> Compile(string line) {
        var parts = line.Split(" ");
        var op = parts[0];
        var args = parts.Skip(1).Select(long.Parse).ToArray();
        return op switch {
            "addr" => regs => regs[args[2]] = regs[args[0]] + regs[args[1]],
            "addi" => regs => regs[args[2]] = regs[args[0]] + args[1],
            "mulr" => regs => regs[args[2]] = regs[args[0]] * regs[args[1]],
            "muli" => regs => regs[args[2]] = regs[args[0]] * args[1],
            "banr" => regs => regs[args[2]] = regs[args[0]] & regs[args[1]],
            "bani" => regs => regs[args[2]] = regs[args[0]] & args[1],
            "borr" => regs => regs[args[2]] = regs[args[0]] | regs[args[1]],
            "bori" => regs => regs[args[2]] = regs[args[0]] | args[1],
            "setr" => regs => regs[args[2]] = regs[args[0]],
            "seti" => regs => regs[args[2]] = args[0],
            "gtir" => regs => regs[args[2]] = args[0] > regs[args[1]] ? 1 : 0,
            "gtri" => regs => regs[args[2]] = regs[args[0]] > args[1] ? 1 : 0,
            "gtrr" => regs => regs[args[2]] = regs[args[0]] > regs[args[1]] ? 1 : 0,
            "eqir" => regs => regs[args[2]] = args[0] == regs[args[1]] ? 1 : 0,
            "eqri" => regs => regs[args[2]] = regs[args[0]] == args[1] ? 1 : 0,
            "eqrr" => regs => regs[args[2]] = regs[args[0]] == regs[args[1]] ? 1 : 0,
            _ => throw new ArgumentException()
        };
    }
}

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