AOC 2020 Day 08

#load "xunit"
#load "..\AOC Connector"
#load "..\AOC 2d Array"

void Main()
{
    RunTests();  // Call RunTests() or press Alt+Shift+T to initiate testing.

    //get aoc data
    var aoc = new AdventOfCode(2020, 8);

    //solve A
    aoc.SubmitAnswer(SolveA(aoc.InputLines), Part.A);

    //solve B
    aoc.SubmitAnswer(SolveB(aoc.InputLines), Part.B);
}

public int SolveA(string[] input = null)
{
    //create and run game
    var game = new GameBoy(input);
    game.Go();
    //answer
    return game.Accumulator;
}

public int SolveB(string[] input)
{
    var game = new GameBoy(input);

    for (int i = 0; i < game.Program.Count; i++)
    {
        var step = game.Program[i];
        if(step.instruction is Argument.nop or Argument.jmp)
        {

                //switch the instruction
                game.Program[i] = (step.instruction == Argument.jmp ? Argument.nop : Argument.jmp, step.value);

                //run the program
                if(game.Go())
                    return game.Accumulator; //SUCCES

                //restore the old instruction
                game.Program[i] = step;
        }
    }
    throw new Exception("Nothing found");
}

public enum Argument
{
    nop, acc, jmp
}


public class GameBoy
{
    /// <summary> Contains all the steps in the program </summary>
    public List<(Argument instruction, int value)> Program;

    public int StepsDoneCounter  {get; private set;}
    public int Accumulator {get; private set;}
    public int ProgramPosition  {get; private set;}

    /// <summary> Constructor </summary>
    public GameBoy(string[] lines)
    {
        this.Program = lines
            .Select(x => x.Split(' ', StringSplitOptions.RemoveEmptyEntries)) //split entries and remove empty
            .Select(x=> ((Argument)Enum.Parse(typeof(Argument), x[0]), int.Parse(x[1]))) //create instruction
            .ToList();
    }

    /// <summary> Track seen items </summary>
    HashSet<int > StepsSeen = new HashSet<int>();

    public bool Go()
    {
        //remove seen
        StepsSeen.Clear();

        //create counters
        StepsDoneCounter = 0;
        Accumulator = 0;
        ProgramPosition = 0;

        //loop through the program
        while(ProgramPosition < this.Program.Count)
        {
            StepsDoneCounter++;

            var step = Program[ProgramPosition];
            //$"[{stepsDoneCounter:D3}] [{position:D2}] {step.instruction} {step.value}".Dump();

            //check if we havent seen this address before
            if (StepsSeen.Contains(ProgramPosition))
            {
                //finished in a infinite loop
                return false;
            }
            StepsSeen.Add(ProgramPosition);

            //what todo
            switch (step.instruction)
            {
                case Argument.acc: Accumulator += step.value; break;
                case Argument.jmp: ProgramPosition += step.value; continue;
                case Argument.nop: break;
            }
            //next instruction
            ProgramPosition++;
        }
        //finished properly
        return true;
    }
}

#region private::Tests
#region test data
string[] testData = new []
{
"nop +0",
"acc +1",
"jmp +4",
"acc +3",
"jmp -3",
"acc -99",
"acc +1",
"jmp -4",
"acc +6",
};

#endregion
//tests
[Fact] void TestA1() => Assert.Equal(005, SolveA(testData));
[Fact] void TestB1() => Assert.Equal(008, SolveB(testData));
//[Fact] void TestB2() => Assert.Equal(126, SolveB(testdata2));
#endregion