Advent of Code

Neil Smith (AoC++) 46*

   0xffff&2016

--- Day 23: Safe Cracking ---

This is one of the top floors of the nicest tower in EBHQ. The Easter Bunny's private office is here, complete with a safe hidden behind a painting, and who wouldn't hide a star in a safe behind a painting?

The safe has a digital screen and keypad for code entry. A sticky note attached to the safe has a password hint on it: "eggs". The painting is of a large rabbit coloring some eggs. You see 7.

When you go to type the code, though, nothing appears on the display; instead, the keypad comes apart in your hands, apparently having been smashed. Behind it is some kind of socket - one that matches a connector in your prototype computer! You pull apart the smashed keypad and extract the logic circuit, plug it into your computer, and plug your computer into the safe.

Now, you just need to figure out what output the keypad would have sent to the safe. You extract the assembunny code from the logic chip (your puzzle input).

The code looks like it uses almost the same architecture and instruction set that the monorail computer used! You should be able to use the same assembunny interpreter for this as you did there, but with one new instruction:

tgl x toggles the instruction x away (pointing at instructions like jnz does: positive means forward; negative means backward):

For example, given this program:

cpy 2 a
tgl a
tgl a
tgl a
cpy 1 a
dec a
dec a

In this example, the final value in register a is 3.

The rest of the electronics seem to place the keypad entry (the number of eggs, 7) in register a, run the code, and then send the value left in register a to the safe.

What value should be sent to the safe?

Your puzzle answer was 14346.

--- Part Two ---

The safe doesn't open, but it does make several angry noises to express its frustration.

You're quite sure your logic is working correctly, so the only other thing is... you check the painting again. As it turns out, colored eggs are still eggs. Now you count 12.

As you run the program with this new input, the prototype computer begins to overheat. You wonder what's taking so long, and whether the lack of any instruction more powerful than "add one" has anything to do with it. Don't bunnies usually multiply?

Anyway, what value should actually be sent to the safe?

Your puzzle answer was 479010906.

Both parts of this puzzle are complete! They provide two gold stars: **

At this point, you should return to your advent calendar and try another puzzle.

If you still want to see it, you can get your puzzle input.

You can also this puzzle.