67 lines
3.7 KiB
Text
67 lines
3.7 KiB
Text
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\--- Day 23: Safe Cracking ---
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----------
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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?
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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`.
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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](11)! You pull apart the smashed keypad and extract the logic circuit, plug it into your computer, and plug your computer into the safe.
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Now, you just need to figure out what output the keypad would have sent to the safe. You extract the [assembunny code](12) from the logic chip (your puzzle input).
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The code looks like it uses *almost* the same architecture and instruction set that the [monorail computer](12) used! You should be able to *use the same assembunny interpreter* for this as you did there, but with one new instruction:
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`tgl x` *toggles* the instruction `x` away (pointing at instructions like `jnz` does: positive means forward; negative means backward):
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* For *one-argument* instructions, `inc` becomes `dec`, and all other one-argument instructions become `inc`.
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* For *two-argument* instructions, `jnz` becomes `cpy`, and all other two-instructions become `jnz`.
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* The arguments of a toggled instruction are *not affected*.
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* If an attempt is made to toggle an instruction outside the program, *nothing happens*.
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* If toggling produces an *invalid instruction* (like `cpy 1 2`) and an attempt is later made to execute that instruction, *skip it instead*.
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* If `tgl` toggles *itself* (for example, if `a` is `0`, `tgl a` would target itself and become `inc a`), the resulting instruction is not executed until the next time it is reached.
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For example, given this program:
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```
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cpy 2 a
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tgl a
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tgl a
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tgl a
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cpy 1 a
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dec a
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dec a
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```
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* `cpy 2 a` initializes register `a` to `2`.
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* The first `tgl a` toggles an instruction `a` (`2`) away from it, which changes the third `tgl a` into `inc a`.
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* The second `tgl a` also modifies an instruction `2` away from it, which changes the `cpy 1 a` into `jnz 1 a`.
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* The fourth line, which is now `inc a`, increments `a` to `3`.
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* Finally, the fifth line, which is now `jnz 1 a`, jumps `a` (`3`) instructions ahead, skipping the `dec a` instructions.
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In this example, the final value in register `a` is `3`.
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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.
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*What value* should be sent to the safe?
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Your puzzle answer was `12654`.
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\--- Part Two ---
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----------
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The safe doesn't open, but it *does* make several angry noises to express its frustration.
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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`.
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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*?
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Anyway, *what value* should actually be sent to the safe?
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Your puzzle answer was `479009214`.
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Both parts of this puzzle are complete! They provide two gold stars: \*\*
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At this point, all that is left is for you to [admire your Advent calendar](/2016).
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If you still want to see it, you can [get your puzzle input](23/input).
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