2016-12-12 14:43:14 +00:00
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Advent of Code
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--- Day 12: Leonardo's Monorail ---
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2018-03-15 16:24:23 +00:00
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You finally reach the top floor of this building: a garden with a slanted
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glass ceiling. Looks like there are no more stars to be had.
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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While sitting on a nearby bench amidst some tiger lilies, you manage to
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decrypt some of the files you extracted from the servers downstairs.
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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According to these documents, Easter Bunny HQ isn't just this building -
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it's a collection of buildings in the nearby area. They're all connected by
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a local monorail, and there's another building not far from here!
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Unfortunately, being night, the monorail is currently not operating.
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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You remotely connect to the monorail control systems and discover that the
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boot sequence expects a password. The password-checking logic (your puzzle
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input) is easy to extract, but the code it uses is strange: it's assembunny
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code designed for the new computer you just assembled. You'll have to
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execute the code and get the password.
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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The assembunny code you've extracted operates on four registers (a, b, c,
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and d) that start at 0 and can hold any integer. However, it seems to make
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use of only a few instructions:
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• cpy x y copies x (either an integer or the value of a register) into
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register y.
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2016-12-12 14:43:14 +00:00
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• inc x increases the value of register x by one.
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2018-03-15 16:24:23 +00:00
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2016-12-12 14:43:14 +00:00
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• dec x decreases the value of register x by one.
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2018-03-15 16:24:23 +00:00
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• jnz x y jumps to an instruction y away (positive means forward; negative
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means backward), but only if x is not zero.
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The jnz instruction moves relative to itself: an offset of -1 would continue
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at the previous instruction, while an offset of 2 would skip over the next
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instruction.
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2016-12-12 14:43:14 +00:00
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For example:
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cpy 41 a
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inc a
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inc a
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dec a
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jnz a 2
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dec a
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2018-03-15 16:24:23 +00:00
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The above code would set register a to 41, increase its value by 2, decrease
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its value by 1, and then skip the last dec a (because a is not zero, so the
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jnz a 2 skips it), leaving register a at 42. When you move past the last
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2016-12-12 14:43:14 +00:00
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instruction, the program halts.
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2018-03-15 16:24:23 +00:00
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After executing the assembunny code in your puzzle input, what value is left
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in register a?
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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Your puzzle answer was 318077.
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2016-12-12 14:43:14 +00:00
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--- Part Two ---
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2018-03-15 16:24:23 +00:00
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As you head down the fire escape to the monorail, you notice it didn't
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start; register c needs to be initialized to the position of the ignition
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key.
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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If you instead initialize register c to be 1, what value is now left in
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register a?
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2016-12-12 14:43:14 +00:00
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2018-03-15 16:24:23 +00:00
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Your puzzle answer was 9227731.
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2016-12-12 14:43:14 +00:00
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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/events
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. http://adventofcode.com/2016/settings
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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/stats
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. http://adventofcode.com/2016/sponsors
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. http://adventofcode.com/2016/sponsors
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. https://www.google.com/search?q=tiger+lilies&tbm=isch
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. http://adventofcode.com/2016/day/11
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. https://en.wikipedia.org/wiki/Processor_register
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. https://en.wikipedia.org/wiki/Integer
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. https://en.wikipedia.org/wiki/Instruction_set
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. http://adventofcode.com/2016
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. http://adventofcode.com/2016/day/12/input
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