adventofcode/2024/day14/problem

Advent of Code

--- Day 14: Restroom Redoubt ---

   One of The Historians needs to use the bathroom; fortunately, you know
   there's a bathroom near an unvisited location on their list, and so you're
   all quickly teleported directly to the lobby of Easter Bunny Headquarters.

   Unfortunately, EBHQ seems to have "improved" bathroom security again after
   your last [16]visit. The area outside the bathroom is swarming with
   robots!

   To get The Historian safely to the bathroom, you'll need a way to predict
   where the robots will be in the future. Fortunately, they all seem to be
   moving on the tile floor in predictable straight lines.

   You make a list (your puzzle input) of all of the robots' current
   positions (p) and velocities (v), one robot per line. For example:

 p=0,4 v=3,-3
 p=6,3 v=-1,-3
 p=10,3 v=-1,2
 p=2,0 v=2,-1
 p=0,0 v=1,3
 p=3,0 v=-2,-2
 p=7,6 v=-1,-3
 p=3,0 v=-1,-2
 p=9,3 v=2,3
 p=7,3 v=-1,2
 p=2,4 v=2,-3
 p=9,5 v=-3,-3

   Each robot's position is given as p=x,y where x represents the number of
   tiles the robot is from the left wall and y represents the number of tiles
   from the top wall (when viewed from above). So, a position of p=0,0 means
   the robot is all the way in the top-left corner.

   Each robot's velocity is given as v=x,y where x and y are given in tiles
   per second. Positive x means the robot is moving to the right, and
   positive y means the robot is moving down. So, a velocity of v=1,-2 means
   that each second, the robot moves 1 tile to the right and 2 tiles up.

   The robots outside the actual bathroom are in a space which is 101 tiles
   wide and 103 tiles tall (when viewed from above). However, in this
   example, the robots are in a space which is only 11 tiles wide and 7 tiles
   tall.

   The robots are good at navigating over/under each other (due to a
   combination of springs, extendable legs, and quadcopters), so they can
   share the same tile and don't interact with each other. Visually, the
   number of robots on each tile in this example looks like this:

 1.12.......
 ...........
 ...........
 ......11.11
 1.1........
 .........1.
 .......1...

   These robots have a unique feature for maximum bathroom security: they can
   teleport. When a robot would run into an edge of the space they're in,
   they instead teleport to the other side, effectively wrapping around the
   edges. Here is what robot p=2,4 v=2,-3 does for the first few seconds:

 Initial state:
 ...........
 ...........
 ...........
 ...........
 ..1........
 ...........
 ...........

 After 1 second:
 ...........
 ....1......
 ...........
 ...........
 ...........
 ...........
 ...........

 After 2 seconds:
 ...........
 ...........
 ...........
 ...........
 ...........
 ......1....
 ...........

 After 3 seconds:
 ...........
 ...........
 ........1..
 ...........
 ...........
 ...........
 ...........

 After 4 seconds:
 ...........
 ...........
 ...........
 ...........
 ...........
 ...........
 ..........1

 After 5 seconds:
 ...........
 ...........
 ...........
 .1.........
 ...........
 ...........
 ...........

   The Historian can't wait much longer, so you don't have to simulate the
   robots for very long. Where will the robots be after 100 seconds?

   In the above example, the number of robots on each tile after 100 seconds
   has elapsed looks like this:

 ......2..1.
 ...........
 1..........
 .11........
 .....1.....
 ...12......
 .1....1....

   To determine the safest area, count the number of robots in each quadrant
   after 100 seconds. Robots that are exactly in the middle (horizontally or
   vertically) don't count as being in any quadrant, so the only relevant
   robots are:

 ..... 2..1.
 ..... .....
 1.... .....

 ..... .....
 ...12 .....
 .1... 1....

   In this example, the quadrants contain 1, 3, 4, and 1 robot. Multiplying
   these together gives a total safety factor of 12.

   Predict the motion of the robots in your list within a space which is 101
   tiles wide and 103 tiles tall. What will the safety factor be after
   exactly 100 seconds have elapsed?

   Your puzzle answer was 218965032.

--- Part Two ---

   During the bathroom break, someone notices that these robots seem awfully
   similar to ones built and used at the North Pole. If they're the same type
   of robots, they should have a hard-coded Easter egg: very rarely, most of
   the robots should arrange themselves into a picture of a Christmas tree.

   What is the fewest number of seconds that must elapse for the robots to
   display the Easter egg?

   Your puzzle answer was 7037.

   Both parts of this puzzle are complete! They provide two gold stars: **

   At this point, you should [17]return to your Advent calendar and try
   another puzzle.

   If you still want to see it, you can [18]get your puzzle input.

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