122 lines
4.6 KiB
Plaintext
122 lines
4.6 KiB
Plaintext
Advent of Code
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--- Day 20: Particle Swarm ---
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Suddenly, the GPU contacts you, asking for help. Someone has
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asked it to simulate too many particles, and it won't be able
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to finish them all in time to render the next frame at this
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rate.
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It transmits to you a buffer (your puzzle input) listing each
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particle in order (starting with particle 0, then particle 1,
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particle 2, and so on). For each particle, it provides the X,
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Y, and Z coordinates for the particle's position (p), velocity
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(v), and acceleration (a), each in the format <X,Y,Z>.
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Each tick, all particles are updated simultaneously. A
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particle's properties are updated in the following order:
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* Increase the X velocity by the X acceleration.
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* Increase the Y velocity by the Y acceleration.
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* Increase the Z velocity by the Z acceleration.
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* Increase the X position by the X velocity.
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* Increase the Y position by the Y velocity.
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* Increase the Z position by the Z velocity.
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Because of seemingly tenuous rationale involving z-buffering,
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the GPU would like to know which particle will stay closest to
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position <0,0,0> in the long term. Measure this using the
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Manhattan distance, which in this situation is simply the sum
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of the absolute values of a particle's X, Y, and Z position.
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For example, suppose you are only given two particles, both of
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which stay entirely on the X-axis (for simplicity). Drawing
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the current states of particles 0 and 1 (in that order) with
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an adjacent a number line and diagram of current X positions
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(marked in parenthesis), the following would take place:
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p=< 3,0,0>, v=< 2,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4
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p=< 4,0,0>, v=< 0,0,0>, a=<-2,0,0> (0)(1)
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p=< 4,0,0>, v=< 1,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4
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p=< 2,0,0>, v=<-2,0,0>, a=<-2,0,0> (1) (0)
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p=< 4,0,0>, v=< 0,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4
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p=<-2,0,0>, v=<-4,0,0>, a=<-2,0,0> (1) (0)
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p=< 3,0,0>, v=<-1,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4
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p=<-8,0,0>, v=<-6,0,0>, a=<-2,0,0> (0)
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At this point, particle 1 will never be closer to <0,0,0> than
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particle 0, and so, in the long run, particle 0 will stay
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closest.
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Which particle will stay closest to position <0,0,0> in the
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long term?
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Your puzzle answer was 119.
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The first half of this puzzle is complete! It provides one
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gold star: *
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--- Part Two ---
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To simplify the problem further, the GPU would like to remove
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any particles that collide. Particles collide if their
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positions ever exactly match. Because particles are updated
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simultaneously, more than two particles can collide at the
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same time and place. Once particles collide, they are removed
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and cannot collide with anything else after that tick.
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For example:
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p=<-6,0,0>, v=< 3,0,0>, a=< 0,0,0>
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p=<-4,0,0>, v=< 2,0,0>, a=< 0,0,0> -6 -5 -4 -3 -2 -1 0 1 2 3
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p=<-2,0,0>, v=< 1,0,0>, a=< 0,0,0> (0) (1) (2) (3)
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p=< 3,0,0>, v=<-1,0,0>, a=< 0,0,0>
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p=<-3,0,0>, v=< 3,0,0>, a=< 0,0,0>
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p=<-2,0,0>, v=< 2,0,0>, a=< 0,0,0> -6 -5 -4 -3 -2 -1 0 1 2 3
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p=<-1,0,0>, v=< 1,0,0>, a=< 0,0,0> (0)(1)(2) (3)
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p=< 2,0,0>, v=<-1,0,0>, a=< 0,0,0>
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p=< 0,0,0>, v=< 3,0,0>, a=< 0,0,0>
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p=< 0,0,0>, v=< 2,0,0>, a=< 0,0,0> -6 -5 -4 -3 -2 -1 0 1 2 3
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p=< 0,0,0>, v=< 1,0,0>, a=< 0,0,0> X (3)
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p=< 1,0,0>, v=<-1,0,0>, a=< 0,0,0>
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------destroyed by collision------
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------destroyed by collision------ -6 -5 -4 -3 -2 -1 0 1 2 3
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------destroyed by collision------ (3)
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p=< 0,0,0>, v=<-1,0,0>, a=< 0,0,0>
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In this example, particles 0, 1, and 2 are simultaneously
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destroyed at the time and place marked X. On the next tick,
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particle 3 passes through unharmed.
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How many particles are left after all collisions are resolved?
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Although it hasn't changed, you can still get your puzzle
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input.
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Answer: 471
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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/2017/about
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. http://adventofcode.com/2017/support
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. http://adventofcode.com/2017/events
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. http://adventofcode.com/2017/settings
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. http://adventofcode.com/2017/auth/logout
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. http://adventofcode.com/2017
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. http://adventofcode.com/2017
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. http://adventofcode.com/2017/leaderboard
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. http://adventofcode.com/2017/stats
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. http://adventofcode.com/2017/sponsors
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. http://adventofcode.com/2017/sponsors
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. https://en.wikipedia.org/wiki/Z-buffering
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. https://en.wikipedia.org/wiki/Taxicab_geometry
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. http://adventofcode.com/2017/day/20/input
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