AdventOfCode/2022/Day21CSharp/Advent2022_Day21.cs

using System.Numerics;

var exampleData = new ProblemData("example-input.txt");
var puzzleData = new ProblemData("puzzle-input.txt");

Console.WriteLine("!! === Part01 === !!");
Console.WriteLine("Example root yells: {0}", exampleData.GetMonkeyValuePart01("root"));
Console.WriteLine("Puzzle root yells: {0}", puzzleData.GetMonkeyValuePart01("root"));

Console.WriteLine("!! === Part02 === !!");
Console.WriteLine("Example human yells: {0}", exampleData.GetMonkeyValuePart02());
Console.WriteLine("Puzzle human yells: {0}", puzzleData.GetMonkeyValuePart02());

abstract class MonkeyCommand
{
    public MonkeyCommand(string name)
    {
        Name = name;
    }

    public abstract BigInteger GetValue();

    public string Name { get; protected set; }

    public static bool DebugPrint { get; set; } = false;
}

class MonkeyYellCommand
    : MonkeyCommand
{
    public MonkeyYellCommand(string name, BigInteger val)
        : base(name)
    {
        Value = val;
    }

    public BigInteger Value { get; set; }
    public override BigInteger GetValue()
    {
        return Value;
    }
}

class MonkeyMathCommand
    : MonkeyCommand
{
    public MonkeyMathCommand(string name, Dictionary<string, MonkeyCommand> lookupTable, string left, string right, char op)
        : base(name)
    {
        LookupTable = lookupTable;
        Left = left;
        Right = right;
        if ((op != '-') && (op != '+') && (op != '*') && (op != '/') && (op != '=')) throw new InvalidDataException();
        Op = op;
    }

    public string Left { get; set; }
    public string Right { get; set; }

    public BigInteger RightValue
    {
        get
        {
            return LookupTable[Right].GetValue();
        }
    }

    public BigInteger LeftValue
    {
        get
        {
            return LookupTable[Left].GetValue();
        }
    }

    public char Op { get; set; }

    public char InverseOp
    {
        get
        {
            switch (Op)
            {
                case '+': return '-';
                case '-': return '+';
                case '*': return '/';
                case '/': return '*';
                default: throw new InvalidDataException();
            }
        }
    }

    public Dictionary<string, MonkeyCommand> LookupTable { get; set; }

    public override BigInteger GetValue()
    {
        BigInteger left = LeftValue;
        BigInteger right = RightValue;

        switch (Op)
        {
            case '+':
                return left + right;
            case '-':
                return left - right;
            case '*':
                return left * right;
            case '/':
                return left / right;
            case '=':
                if (MonkeyCommand.DebugPrint && LookupTable["humn"].GetValue()%10000 == 0) Console.WriteLine("Comparing {0} v {1} with humn {2}", left, right, LookupTable["humn"].GetValue());
                return left - right;
            default: throw new InvalidDataException();

        }
    }
}

class ProblemData
{
    private Dictionary<string, MonkeyCommand>   CommandLookupPart01 { get; set; }
    private Dictionary<string, MonkeyCommand>   CommandLookupPart02 { get; set; }

    public ProblemData(string filename)
    {
        CommandLookupPart01 = new Dictionary<string, MonkeyCommand>();
        CommandLookupPart02 = new Dictionary<string, MonkeyCommand>();

        using (StreamReader reader = System.IO.File.OpenText(filename))
        {
            while (!reader.EndOfStream)
            {
                var line = reader.ReadLine();
                if (line == null) throw new InvalidDataException();

                var split = line.Split(':', StringSplitOptions.TrimEntries);
                var name = split[0];

                MonkeyCommand monkey, monkey2;

                // First see if its a value being yelled by the goddamned monkeys
                int val;
                if (int.TryParse(split[1], out val))
                {
                    // It's a value monkey
                    monkey = new MonkeyYellCommand(name, val);
                    monkey2 = new MonkeyYellCommand(name, val);
                }
                else
                {
                    // It's a math monkey
                    var mathline = split[1].Split(' ', StringSplitOptions.RemoveEmptyEntries);
                    monkey = new MonkeyMathCommand(name, CommandLookupPart01, mathline[0], mathline[2], mathline[1][0]);

                    char op = mathline[1][0];
                    if (name == "root")
                        op = '=';
                    monkey2 = new MonkeyMathCommand(name, CommandLookupPart02, mathline[0], mathline[2], op);
                }

                CommandLookupPart01[name] = monkey;
                CommandLookupPart02[name] = monkey2;
            }
        }
    }

    public BigInteger GetMonkeyValuePart01(string name)
    {
        return CommandLookupPart01[name].GetValue();
    }

    public BigInteger GetMonkeyValuePart02()
    {
        MonkeyMathCommand rootCmd = (MonkeyMathCommand)CommandLookupPart02["root"];

        // Find the side the human is on
        bool isHumanOnLeft = IsHumanOnLeft(CommandLookupPart02, rootCmd);
        BigInteger targetValue;

        if (isHumanOnLeft)
        {
            targetValue = rootCmd.RightValue;
        }
        else
        {
            targetValue = rootCmd.LeftValue;
        }

        var humnCmd = (MonkeyYellCommand)CommandLookupPart02["humn"];
        BigInteger result = 0;
        BigInteger high = long.MaxValue, low = long.MinValue;
        BigInteger mid = low + (high - low) / 2;

        bool incrementUp = false;
        humnCmd.Value = 1;
        var first = isHumanOnLeft ? rootCmd.LeftValue : rootCmd.RightValue;
        humnCmd.Value = 100;
        var second = isHumanOnLeft ? rootCmd.LeftValue : rootCmd.RightValue;

        if (second > first) incrementUp = true;

        while ((isHumanOnLeft ? rootCmd.LeftValue : rootCmd.RightValue) != targetValue)
        {
            humnCmd.Value = mid;

            var newVal = isHumanOnLeft ? rootCmd.LeftValue : rootCmd.RightValue;

            if ((incrementUp && (newVal > targetValue)) || (!incrementUp && (newVal < targetValue)))
            {
                high = low + (high - low) / 2;
            }
            else
            {
                low = low + (high - low) / 2;
            }

            mid = low + (high - low) / 2;
        }

        return CommandLookupPart02["humn"].GetValue();
    }

    private static bool IsHumanOnLeft(Dictionary<string,MonkeyCommand> dict, MonkeyMathCommand command)
    {
        MonkeyYellCommand humnCmd = (MonkeyYellCommand)dict["humn"];

        var ogRight = command.RightValue;
        var ogLeft = command.LeftValue;

        humnCmd.Value += 10;

        var newRight = command.RightValue;
        var newLeft = command.LeftValue;

        humnCmd.Value -= 10;

        if (ogLeft == newLeft) return false;
        else if (ogRight == newRight) return true;
        else throw new InvalidDataException();
    }
        
}