public int ComputePart2(IEnumerable <Instruction> input = null)
{
var instructions = (input ?? Instructions)
.Select(x => new { Instruction = x, State = new Day8.InstructionState() })
.ToArray();
var state = new Day8.MachineState();
var visitedInstructions = new List <int>();
while (!instructions[state.InstructionPointer].State.Visited)
{
visitedInstructions.Add(state.InstructionPointer);
var cell = instructions[state.InstructionPointer];
state = cell.Instruction.Execute(state);
cell.State.Visited = true;
}
var instructionsToSwap = visitedInstructions
.Where(x => instructions[x].Instruction is Jmp || instructions[x].Instruction is Nop);
var instructionSets = instructionsToSwap
.Select(x => {
var newSet = instructions.Select(x => x.Instruction).ToArray();
newSet[x] = newSet[x].SwapJmpAndNop();
return(newSet);
});
return(instructionSets
.Select(AttemptHalt)
.First(x => x.HasValue)
.Value);
}
private int ComputePart1()
{
var instructions = Instructions
.Select(x => new { Instruction = x, State = new Day8.InstructionState() })
.ToArray();
var state = new Day8.MachineState();
var iterations = 0;
while (!instructions[state.InstructionPointer].State.Visited)
{
iterations++;
var cell = instructions[state.InstructionPointer];
state = cell.Instruction.Execute(state);
cell.State.Visited = true;
}
return(state.Accumulator);
}
private int?AttemptHalt(IEnumerable <Instruction> instructions)
{
var cells = instructions
.Select(x => new { Instruction = x, State = new Day8.InstructionState() })
.ToArray();
var state = new Day8.MachineState();
while (state.InstructionPointer < cells.Length && !cells[state.InstructionPointer].State.Visited)
{
var cell = cells[state.InstructionPointer];
state = cell.Instruction.Execute(state);
cell.State.Visited = true;
}
if (state.InstructionPointer == cells.Count())
{
return(state.Accumulator);
}
return(null);
}