private static BootProgram ReadProgram(List <string> lines)
{
var program = new BootProgram();
foreach (var line in lines)
{
var instruction = ReadInstruction(line);
program.Instructions.Add(instruction);
}
return(program);
}
public static long Part1(BootProgram program)
{
if (program == null)
{
throw new ArgumentNullException(nameof(program));
}
var machine = new Machine(program);
machine.Run();
return(machine.Acc);
}
private static bool ExecuteProgram(BootProgram program)
{
// Reset execution state
foreach (var instruction in program.Instructions)
{
instruction.IsExecuted = false;
}
program.State.Accumulator = 0;
var ip = 0;
var instructions = program.Instructions;
var state = program.State;
while (ip < instructions.Count)
{
var instruction = instructions[ip];
if (instruction.IsExecuted)
{
return(false); // we stop but didn't finish
}
instruction.IsExecuted = true;
switch (instruction.Operation)
{
case "nop":
{
ip++;
break;
}
case "acc":
{
state.Accumulator += instruction.Argument;
ip++;
break;
}
case "jmp":
{
ip += instruction.Argument;
break;
}
default:
throw new Exception($"Unpexpected instruction: {instruction.Operation}");
}
}
return(true);
}
private static bool PatchProgram(BootProgram program, int patchIndex)
{
// Only works after executing once, we find the latest executed jmp instruction and patch to nop
var lastInstruction = program.Instructions.AsEnumerable()?.Skip(patchIndex).FirstOrDefault(i => i.Operation == "jmp" || i.Operation == "nop");
if (lastInstruction == null)
{
throw new Exception($"Found no more instructions to patch (patched {patchIndex + 1}");
}
// Patch and check if we finish now
PatchOperation(lastInstruction);
var result = ExecuteProgram(program);
PatchOperation(lastInstruction); // Patch it back, so the next run gets a clean app
return(result);
}
public static int Main(string[] args)
{
if (args == null)
{
throw new ArgumentNullException(nameof(args));
}
string filename = args.Length > 0 ? args[0] : "input.txt";
if (!File.Exists(filename))
{
Console.Error.WriteLine($"File not found: {filename}");
return(100);
}
BootProgram program = BootProgram.FromString(File.ReadAllText(filename));
Console.WriteLine(Solver.Part1(program));
Console.WriteLine(Solver.Part2(program));
return(0);
}
public static long Part2(BootProgram program)
{
if (program == null)
{
throw new ArgumentNullException(nameof(program));
}
var machine = new Machine(program);
int ptrPatch = -1;
while (!machine.Run())
{
// Patch program
var patchedProgram = new BootProgram(program.Instructions);
while (true)
{
ptrPatch += 1;
Instruction instruction = patchedProgram.Instructions[ptrPatch];
if (instruction.OpCode == OpCode.Jmp)
{
patchedProgram.Patch(ptrPatch, new Instruction(OpCode.Nop, instruction.Arg));
break;
}
else if (instruction.OpCode == OpCode.Nop)
{
patchedProgram.Patch(ptrPatch, new Instruction(OpCode.Jmp, instruction.Arg));
break;
}
}
// Initialize new machine with patched program
machine = new Machine(patchedProgram);
}
return(machine.Acc);
}
public Machine(BootProgram program) => _program = program;
