Add 2019 Problems
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2019/day21/problem
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2019/day21/problem
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Advent of Code
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--- Day 21: Springdroid Adventure ---
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You lift off from Pluto and start flying in the direction of Santa.
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While experimenting further with the tractor beam, you accidentally pull an asteroid directly into your ship! It deals
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significant damage to your hull and causes your ship to begin tumbling violently.
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You can send a droid out to investigate, but the tumbling is causing enough artificial gravity that one wrong step could send
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the droid through a hole in the hull and flying out into space.
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The clear choice for this mission is a droid that can jump over the holes in the hull - a springdroid.
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You can use an Intcode program (your puzzle input) running on an ASCII-capable computer to program the springdroid. However,
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springdroids don't run Intcode; instead, they run a simplified assembly language called springscript.
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While a springdroid is certainly capable of navigating the artificial gravity and giant holes, it has one downside: it can
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only remember at most 15 springscript instructions.
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The springdroid will move forward automatically, constantly thinking about whether to jump. The springscript program defines
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the logic for this decision.
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Springscript programs only use Boolean values, not numbers or strings. Two registers are available: T, the temporary value
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register, and J, the jump register. If the jump register is true at the end of the springscript program, the springdroid will
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try to jump. Both of these registers start with the value false.
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Springdroids have a sensor that can detect whether there is ground at various distances in the direction it is facing; these
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values are provided in read-only registers. Your springdroid can detect ground at four distances: one tile away (A), two
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tiles away (B), three tiles away (C), and four tiles away (D). If there is ground at the given distance, the register will be
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true; if there is a hole, the register will be false.
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There are only three instructions available in springscript:
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• AND X Y sets Y to true if both X and Y are true; otherwise, it sets Y to false.
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• OR X Y sets Y to true if at least one of X or Y is true; otherwise, it sets Y to false.
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• NOT X Y sets Y to true if X is false; otherwise, it sets Y to false.
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In all three instructions, the second argument (Y) needs to be a writable register (either T or J). The first argument (X)
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can be any register (including A, B, C, or D).
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For example, the one-instruction program NOT A J means "if the tile immediately in front of me is not ground, jump".
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Or, here is a program that jumps if a three-tile-wide hole (with ground on the other side of the hole) is detected:
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NOT A J
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NOT B T
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AND T J
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NOT C T
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AND T J
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AND D J
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The Intcode program expects ASCII inputs and outputs. It will begin by displaying a prompt; then, input the desired
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instructions one per line. End each line with a newline (ASCII code 10). When you have finished entering your program,
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provide the command WALK followed by a newline to instruct the springdroid to begin surveying the hull.
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If the springdroid falls into space, an ASCII rendering of the last moments of its life will be produced. In these, @ is the
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springdroid, # is hull, and . is empty space. For example, suppose you program the springdroid like this:
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NOT D J
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WALK
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This one-instruction program sets J to true if and only if there is no ground four tiles away. In other words, it attempts to
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jump into any hole it finds:
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.................
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.................
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@................
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#####.###########
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.................
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.................
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.@...............
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#####.###########
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.................
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..@..............
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.................
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#####.###########
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...@.............
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.................
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.................
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#####.###########
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.................
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....@............
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.................
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#####.###########
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.................
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.................
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.....@...........
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#####.###########
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.................
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.................
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.................
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#####@###########
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However, if the springdroid successfully makes it across, it will use an output instruction to indicate the amount of damage
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to the hull as a single giant integer outside the normal ASCII range.
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Program the springdroid with logic that allows it to survey the hull without falling into space. What amount of hull damage
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does it report?
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Your puzzle answer was 19354818.
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--- Part Two ---
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There are many areas the springdroid can't reach. You flip through the manual and discover a way to increase its sensor
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range.
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Instead of ending your springcode program with WALK, use RUN. Doing this will enable extended sensor mode, capable of sensing
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ground up to nine tiles away. This data is available in five new read-only registers:
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• Register E indicates whether there is ground five tiles away.
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• Register F indicates whether there is ground six tiles away.
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• Register G indicates whether there is ground seven tiles away.
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• Register H indicates whether there is ground eight tiles away.
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• Register I indicates whether there is ground nine tiles away.
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All other functions remain the same.
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Successfully survey the rest of the hull by ending your program with RUN. What amount of hull damage does the springdroid now
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report?
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Your puzzle answer was 1143787220.
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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.
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If you still want to see it, you can get your puzzle input.
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2019/about
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. https://adventofcode.com/2019/events
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. https://adventofcode.com/2019/settings
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. https://adventofcode.com/2019/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2019/support
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. https://adventofcode.com/2019
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. https://adventofcode.com/2019
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. https://adventofcode.com/2019/support
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. https://adventofcode.com/2019/sponsors
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. https://adventofcode.com/2019/leaderboard
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. https://adventofcode.com/2019/stats
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. https://adventofcode.com/2019/sponsors
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. https://en.wikipedia.org/wiki/Artificial_gravity
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. https://adventofcode.com/2019/day/9
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. https://adventofcode.com/2019/day/17
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. https://en.wikipedia.org/wiki/Programmable_read-only_memory
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. https://en.wikipedia.org/wiki/Boolean_data_type
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. https://adventofcode.com/2019
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. https://adventofcode.com/2019/day/21/input
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