194 lines
5.4 KiB
Plaintext
194 lines
5.4 KiB
Plaintext
Advent of Code
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--- Day 14: Restroom Redoubt ---
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One of The Historians needs to use the bathroom; fortunately, you know
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there's a bathroom near an unvisited location on their list, and so you're
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all quickly teleported directly to the lobby of Easter Bunny Headquarters.
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Unfortunately, EBHQ seems to have "improved" bathroom security again after
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your last [16]visit. The area outside the bathroom is swarming with
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robots!
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To get The Historian safely to the bathroom, you'll need a way to predict
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where the robots will be in the future. Fortunately, they all seem to be
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moving on the tile floor in predictable straight lines.
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You make a list (your puzzle input) of all of the robots' current
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positions (p) and velocities (v), one robot per line. For example:
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p=0,4 v=3,-3
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p=6,3 v=-1,-3
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p=10,3 v=-1,2
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p=2,0 v=2,-1
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p=0,0 v=1,3
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p=3,0 v=-2,-2
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p=7,6 v=-1,-3
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p=3,0 v=-1,-2
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p=9,3 v=2,3
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p=7,3 v=-1,2
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p=2,4 v=2,-3
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p=9,5 v=-3,-3
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Each robot's position is given as p=x,y where x represents the number of
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tiles the robot is from the left wall and y represents the number of tiles
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from the top wall (when viewed from above). So, a position of p=0,0 means
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the robot is all the way in the top-left corner.
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Each robot's velocity is given as v=x,y where x and y are given in tiles
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per second. Positive x means the robot is moving to the right, and
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positive y means the robot is moving down. So, a velocity of v=1,-2 means
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that each second, the robot moves 1 tile to the right and 2 tiles up.
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The robots outside the actual bathroom are in a space which is 101 tiles
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wide and 103 tiles tall (when viewed from above). However, in this
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example, the robots are in a space which is only 11 tiles wide and 7 tiles
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tall.
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The robots are good at navigating over/under each other (due to a
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combination of springs, extendable legs, and quadcopters), so they can
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share the same tile and don't interact with each other. Visually, the
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number of robots on each tile in this example looks like this:
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1.12.......
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...........
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...........
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......11.11
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1.1........
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.........1.
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.......1...
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These robots have a unique feature for maximum bathroom security: they can
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teleport. When a robot would run into an edge of the space they're in,
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they instead teleport to the other side, effectively wrapping around the
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edges. Here is what robot p=2,4 v=2,-3 does for the first few seconds:
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Initial state:
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...........
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...........
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...........
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...........
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..1........
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...........
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...........
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After 1 second:
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...........
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....1......
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...........
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...........
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...........
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...........
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...........
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After 2 seconds:
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...........
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...........
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...........
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...........
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...........
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......1....
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...........
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After 3 seconds:
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...........
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...........
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........1..
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...........
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...........
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...........
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...........
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After 4 seconds:
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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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..........1
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After 5 seconds:
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...........
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...........
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...........
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.1.........
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...........
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...........
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...........
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The Historian can't wait much longer, so you don't have to simulate the
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robots for very long. Where will the robots be after 100 seconds?
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In the above example, the number of robots on each tile after 100 seconds
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has elapsed looks like this:
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......2..1.
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...........
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1..........
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.11........
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.....1.....
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...12......
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.1....1....
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To determine the safest area, count the number of robots in each quadrant
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after 100 seconds. Robots that are exactly in the middle (horizontally or
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vertically) don't count as being in any quadrant, so the only relevant
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robots are:
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..... 2..1.
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..... .....
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1.... .....
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..... .....
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...12 .....
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.1... 1....
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In this example, the quadrants contain 1, 3, 4, and 1 robot. Multiplying
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these together gives a total safety factor of 12.
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Predict the motion of the robots in your list within a space which is 101
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tiles wide and 103 tiles tall. What will the safety factor be after
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exactly 100 seconds have elapsed?
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Your puzzle answer was 218965032.
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--- Part Two ---
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During the bathroom break, someone notices that these robots seem awfully
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similar to ones built and used at the North Pole. If they're the same type
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of robots, they should have a hard-coded Easter egg: very rarely, most of
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the robots should arrange themselves into a picture of a Christmas tree.
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What is the fewest number of seconds that must elapse for the robots to
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display the Easter egg?
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Your puzzle answer was 7037.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should [17]return to your Advent calendar and try
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another puzzle.
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If you still want to see it, you can [18]get your puzzle input.
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References
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Visible links
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1. https://adventofcode.com/
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2. https://adventofcode.com/2024/about
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3. https://adventofcode.com/2024/events
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4. https://cottonbureau.com/people/advent-of-code
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5. https://adventofcode.com/2024/settings
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6. https://adventofcode.com/2024/auth/logout
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7. Advent of Code Supporter
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https://adventofcode.com/2024/support
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8. https://adventofcode.com/2024
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9. https://adventofcode.com/2024
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10. https://adventofcode.com/2024/support
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12. https://adventofcode.com/2024/leaderboard
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13. https://adventofcode.com/2024/stats
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16. https://adventofcode.com/2016/day/2
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17. https://adventofcode.com/2024
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18. https://adventofcode.com/2024/day/14/input
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