public string Solve(string input)
{
string[] rows = input.Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
int instructionPointerRegister = int.Parse(rows[0].Split(' ')[1]);
int instructionPointer = 0;
Instruction[] instructions = rows
.Skip(1)
.Select(Parser.BuildInstructionFromInputLine)
.ToArray();
var operations = Operation.All.ToDictionary(x => x.Name, x => x.Execute);
int[] registers = new[] { 0, 0, 0, 0, 0, 0 };
var seenR2Values = new List <int>(1000000);
// We can assume from the question that r2 is going to change, and at some point we're going to
// hit a loop. Therefore we need to watch the comparisons, store the values from r2, and the
// first time we see a number crop up twice, we know the answer is the previous value we stored.
while (instructionPointer >= 0 && instructionPointer < instructions.Length)
{
////Console.Write($"{instructionPointer}:{registers[0]}:{registers[1]}:{registers[2]}:{registers[3]}:{registers[4]}:{registers[5]:D4}:");
if (instructionPointer == 30)
{
if (seenR2Values.Contains(registers[2]))
{
return(seenR2Values.Last().ToString());
}
seenR2Values.Add(registers[2]);
}
registers[instructionPointerRegister] = instructionPointer;
Instruction targetInstruction = instructions[instructionPointer];
////Console.Write($"{targetInstruction.OpName}:{targetInstruction.A}:{targetInstruction.B}:{targetInstruction.C}:");
operations[targetInstruction.OpName](registers, targetInstruction);
instructionPointer = registers[instructionPointerRegister];
instructionPointer++;
////Console.WriteLine($"{registers[0]:D4}:{registers[1]:D4}:{registers[2]:D4}:{registers[3]:D4}:{registers[4]:D4}:{registers[5]:D4}");
}
return(string.Empty);
}
public string Solve(string input)
{
string[] rows = input.Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
int instructionPointerRegister = int.Parse(rows[0].Split(' ')[1]);
int instructionPointer = 0;
Instruction[] instructions = rows
.Skip(1)
.Select(Parser.BuildInstructionFromInputLine)
.ToArray();
var operations = Operation.All.ToDictionary(x => x.Name, x => x.Execute);
int[] registers = new[] { 0, 0, 0, 0, 0, 0 };
// From looking at the program, r0 is only used for one check - in line 30, and if it's equal
// at that point to the value in r2 then the program will exit. So we need to know what the
// value of r2 is the first time we execute line 30
while (instructionPointer >= 0 && instructionPointer < instructions.Length)
{
////Console.Write($"{instructionPointer}:{registers[0]}:{registers[1]}:{registers[2]}:{registers[3]}:{registers[4]}:{registers[5]:D4}:");
if (instructionPointer == 30)
{
return(registers[2].ToString());
}
registers[instructionPointerRegister] = instructionPointer;
Instruction targetInstruction = instructions[instructionPointer];
////Console.Write($"{targetInstruction.OpName}:{targetInstruction.A}:{targetInstruction.B}:{targetInstruction.C}:");
operations[targetInstruction.OpName](registers, targetInstruction);
instructionPointer = registers[instructionPointerRegister];
instructionPointer++;
////Console.WriteLine($"{registers[0]:D4}:{registers[1]:D4}:{registers[2]:D4}:{registers[3]:D4}:{registers[4]:D4}:{registers[5]:D4}");
}
return(string.Empty);
}
