Little Jane Marie just got her very first computer for Christmas from some unknown benefactor. It comes with instructions and an example program, but the computer itself seems to be malfunctioning. She's curious what the program does, and would like you to help her run it.

The manual explains that the computer supports two registers and six instructions (truly, it goes on to remind the reader, a state-of-the-art technology). The registers are named a and b, can hold any non-negative integer, and begin with a value of 0. The instructions are as follows:

Read the full puzzle.

using System;
using System.Collections.Generic;

namespace AdventOfCode.Y2015.Day23;

[ProblemName("Opening the Turing Lock")]
class Solution : Solver {

    public object PartOne(string input) => Solve(input, 0);
    public object PartTwo(string input) => Solve(input, 1);

    long Solve(string input, long a) {
        var regs = new Dictionary<string, long>();
        var ip = 0L;
        long getReg(string reg) {
            return long.TryParse(reg, out var n) ? n
                : regs.ContainsKey(reg) ? regs[reg]
                : 0;
        }
        void setReg(string reg, long value) {
            regs[reg] = value;
        }

        setReg("a", a);
        var prog = input.Split('\n');
        while (ip >= 0 && ip < prog.Length) {
            var line = prog[ip];
            var parts = line.Replace(",", "").Split(" ");
            switch (parts[0]) {
                case "hlf":
                    setReg(parts[1], getReg(parts[1]) / 2);
                    ip++;
                    break;
                case "tpl":
                    setReg(parts[1], getReg(parts[1]) * 3);
                    ip++;
                    break;
                case "inc":
                    setReg(parts[1], getReg(parts[1]) + 1);
                    ip++;
                    break;
                case "jmp":
                    ip += getReg(parts[1]);
                    break;
                case "jie":
                    ip += getReg(parts[1]) % 2 == 0 ? getReg(parts[2]) : 1;
                    break;
                case "jio":
                    ip += getReg(parts[1]) == 1 ? getReg(parts[2]) : 1;
                    break;
                default: throw new Exception("Cannot parse " + line);
            }
        }
        return getReg("b");
    }
}

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