121 lines
4.3 KiB
Plaintext
121 lines
4.3 KiB
Plaintext
Advent of Code
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--- Day 23: Safe Cracking ---
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This is one of the top floors of the nicest tower in EBHQ. The Easter
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Bunny's private office is here, complete with a safe hidden behind a
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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
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attached to the safe has a password hint on it: "eggs". The painting is of a
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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;
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instead, the keypad comes apart in your hands, apparently having been
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smashed. Behind it is some kind of socket - one that matches a connector in
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your prototype computer! You pull apart the smashed keypad and extract the
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logic circuit, plug it into your computer, and plug your computer into the
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safe.
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Now, you just need to figure out what output the keypad would have sent to
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the safe. You extract the assembunny code from the logic chip (your puzzle
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input).
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The code looks like it uses almost the same architecture and instruction set
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that the monorail computer used! You should be able to use the same
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assembunny interpreter for this as you did there, but with one new
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instruction:
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tgl x toggles the instruction x away (pointing at instructions like jnz
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does: positive means forward; negative means backward):
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• For one-argument instructions, inc becomes dec, and all other
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one-argument instructions become inc.
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• For two-argument instructions, jnz becomes cpy, and all other
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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,
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nothing happens.
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• If toggling produces an invalid instruction (like cpy 1 2) and an
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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
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and become inc a), the resulting instruction is not executed until the
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next time it is reached.
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For example, given this program:
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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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• 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
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the third tgl a into inc a.
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• The second tgl a also modifies an instruction 2 away from it, which
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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
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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
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eggs, 7) in register a, run the code, and then send the value left in
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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 10584.
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--- Part Two ---
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The safe doesn't open, but it does make several angry noises to express its
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frustration.
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You're quite sure your logic is working correctly, so the only other thing
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is... you check the painting again. As it turns out, colored eggs are still
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eggs. Now you count 12.
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As you run the program with this new input, the prototype computer begins to
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overheat. You wonder what's taking so long, and whether the lack of any
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instruction more powerful than "add one" has anything to do with it. Don't
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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 479007144.
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References
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Visible links
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. http://adventofcode.com/
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. http://adventofcode.com/2016/about
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. http://adventofcode.com/2016/support
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. http://adventofcode.com/2016/auth/logout
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. http://adventofcode.com/2016
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. http://adventofcode.com/2016
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. http://adventofcode.com/2016/leaderboard
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. http://adventofcode.com/2016/sponsors
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. http://adventofcode.com/2016/sponsors
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. http://adventofcode.com/2016/day/11
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. http://adventofcode.com/2016/day/12
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. http://adventofcode.com/2016/day/12
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. http://adventofcode.com/2016
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. http://adventofcode.com/2016/day/23/input
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