adventofcode/2023/day10/problem

                               [1]Advent of Code

     • [2][About]
     • [3][Events]
     • [4][Shop]
     • [5][Settings]
     • [6][Log Out]

   br0xen [7](AoC++) 20*

                                       //[8]2023

     • [9][Calendar]
     • [10][AoC++]
     • [11][Sponsors]
     • [12][Leaderboard]
     • [13][Stats]

   Our [14]sponsors help make Advent of Code possible:
   [15]Kotlin by JetBrains - Jingle bells, Kotlin pals, coding all the way!
   Solve puzzles, catch our daily livestreams for expert guidance, embrace
   the joy of Kotlin, and engage with a fantastic community. Happy holidays
   and happy coding!

--- Day 10: Pipe Maze ---

   You use the hang glider to ride the hot air from Desert Island all the way
   up to the floating metal island. This island is surprisingly cold and
   there definitely aren't any thermals to glide on, so you leave your hang
   glider behind.

   You wander around for a while, but you don't find any people or animals.
   However, you do occasionally find signposts labeled "[16]Hot Springs"
   pointing in a seemingly consistent direction; maybe you can find someone
   at the hot springs and ask them where the desert-machine parts are made.

   The landscape here is alien; even the flowers and trees are made of metal.
   As you stop to admire some metal grass, you notice something metallic
   scurry away in your peripheral vision and jump into a big pipe! It didn't
   look like any animal you've ever seen; if you want a better look, you'll
   need to get ahead of it.

   Scanning the area, you discover that the entire field you're standing on
   is densely packed with pipes; it was hard to tell at first because they're
   the same metallic silver color as the "ground". You make a quick sketch of
   all of the surface pipes you can see (your puzzle input).

   The pipes are arranged in a two-dimensional grid of tiles:

     • | is a vertical pipe connecting north and south.
     • - is a horizontal pipe connecting east and west.
     • L is a 90-degree bend connecting north and east.
     • J is a 90-degree bend connecting north and west.
     • 7 is a 90-degree bend connecting south and west.
     • F is a 90-degree bend connecting south and east.
     • . is ground; there is no pipe in this tile.
     • S is the starting position of the animal; there is a pipe on this
       tile, but your sketch doesn't show what shape the pipe has.

   Based on the acoustics of the animal's scurrying, you're confident the
   pipe that contains the animal is one large, continuous loop.

   For example, here is a square loop of pipe:

 .....
 .F-7.
 .|.|.
 .L-J.
 .....

   If the animal had entered this loop in the northwest corner, the sketch
   would instead look like this:

 .....
 .S-7.
 .|.|.
 .L-J.
 .....

   In the above diagram, the S tile is still a 90-degree F bend: you can tell
   because of how the adjacent pipes connect to it.

   Unfortunately, there are also many pipes that aren't connected to the
   loop! This sketch shows the same loop as above:

 -L|F7
 7S-7|
 L|7||
 -L-J|
 L|-JF

   In the above diagram, you can still figure out which pipes form the main
   loop: they're the ones connected to S, pipes those pipes connect to, pipes
   those pipes connect to, and so on. Every pipe in the main loop connects to
   its two neighbors (including S, which will have exactly two pipes
   connecting to it, and which is assumed to connect back to those two
   pipes).

   Here is a sketch that contains a slightly more complex main loop:

 ..F7.
 .FJ|.
 SJ.L7
 |F--J
 LJ...

   Here's the same example sketch with the extra, non-main-loop pipe tiles
   also shown:

 7-F7-
 .FJ|7
 SJLL7
 |F--J
 LJ.LJ

   If you want to get out ahead of the animal, you should find the tile in
   the loop that is farthest from the starting position. Because the animal
   is in the pipe, it doesn't make sense to measure this by direct distance.
   Instead, you need to find the tile that would take the longest number of
   steps along the loop to reach from the starting point - regardless of
   which way around the loop the animal went.

   In the first example with the square loop:

 .....
 .S-7.
 .|.|.
 .L-J.
 .....

   You can count the distance each tile in the loop is from the starting
   point like this:

 .....
 .012.
 .1.3.
 .234.
 .....

   In this example, the farthest point from the start is 4 steps away.

   Here's the more complex loop again:

 ..F7.
 .FJ|.
 SJ.L7
 |F--J
 LJ...

   Here are the distances for each tile on that loop:

 ..45.
 .236.
 01.78
 14567
 23...

   Find the single giant loop starting at S. How many steps along the loop
   does it take to get from the starting position to the point farthest from
   the starting position?

   Your puzzle answer was 6942.

--- Part Two ---

   You quickly reach the farthest point of the loop, but the animal never
   emerges. Maybe its nest is within the area enclosed by the loop?

   To determine whether it's even worth taking the time to search for such a
   nest, you should calculate how many tiles are contained within the loop.
   For example:

 ...........
 .S-------7.
 .|F-----7|.
 .||.....||.
 .||.....||.
 .|L-7.F-J|.
 .|..|.|..|.
 .L--J.L--J.
 ...........

   The above loop encloses merely four tiles - the two pairs of . in the
   southwest and southeast (marked I below). The middle . tiles (marked O
   below) are not in the loop. Here is the same loop again with those regions
   marked:

 ...........
 .S-------7.
 .|F-----7|.
 .||OOOOO||.
 .||OOOOO||.
 .|L-7OF-J|.
 .|II|O|II|.
 .L--JOL--J.
 .....O.....

   In fact, there doesn't even need to be a full tile path to the outside for
   tiles to count as outside the loop - squeezing between pipes is also
   allowed! Here, I is still within the loop and O is still outside the loop:

 ..........
 .S------7.
 .|F----7|.
 .||OOOO||.
 .||OOOO||.
 .|L-7F-J|.
 .|II||II|.
 .L--JL--J.
 ..........

   In both of the above examples, 4 tiles are enclosed by the loop.

   Here's a larger example:

 .F----7F7F7F7F-7....
 .|F--7||||||||FJ....
 .||.FJ||||||||L7....
 FJL7L7LJLJ||LJ.L-7..
 L--J.L7...LJS7F-7L7.
 ....F-J..F7FJ|L7L7L7
 ....L7.F7||L7|.L7L7|
 .....|FJLJ|FJ|F7|.LJ
 ....FJL-7.||.||||...
 ....L---J.LJ.LJLJ...

   The above sketch has many random bits of ground, some of which are in the
   loop (I) and some of which are outside it (O):

 OF----7F7F7F7F-7OOOO
 O|F--7||||||||FJOOOO
 O||OFJ||||||||L7OOOO
 FJL7L7LJLJ||LJIL-7OO
 L--JOL7IIILJS7F-7L7O
 OOOOF-JIIF7FJ|L7L7L7
 OOOOL7IF7||L7|IL7L7|
 OOOOO|FJLJ|FJ|F7|OLJ
 OOOOFJL-7O||O||||OOO
 OOOOL---JOLJOLJLJOOO

   In this larger example, 8 tiles are enclosed by the loop.

   Any tile that isn't part of the main loop can count as being enclosed by
   the loop. Here's another example with many bits of junk pipe lying around
   that aren't connected to the main loop at all:

 FF7FSF7F7F7F7F7F---7
 L|LJ||||||||||||F--J
 FL-7LJLJ||||||LJL-77
 F--JF--7||LJLJ7F7FJ-
 L---JF-JLJ.||-FJLJJ7
 |F|F-JF---7F7-L7L|7|
 |FFJF7L7F-JF7|JL---7
 7-L-JL7||F7|L7F-7F7|
 L.L7LFJ|||||FJL7||LJ
 L7JLJL-JLJLJL--JLJ.L

   Here are just the tiles that are enclosed by the loop marked with I:

 FF7FSF7F7F7F7F7F---7
 L|LJ||||||||||||F--J
 FL-7LJLJ||||||LJL-77
 F--JF--7||LJLJIF7FJ-
 L---JF-JLJIIIIFJLJJ7
 |F|F-JF---7IIIL7L|7|
 |FFJF7L7F-JF7IIL---7
 7-L-JL7||F7|L7F-7F7|
 L.L7LFJ|||||FJL7||LJ
 L7JLJL-JLJLJL--JLJ.L

   In this last example, 10 tiles are enclosed by the loop.

   Figure out whether you have time to search for the nest by calculating the
   area within the loop. How many tiles are enclosed by the loop?

   Your puzzle answer was 297.

   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.

   You can also [Shareon [19]Twitter [20]Mastodon] this puzzle.

References

   Visible links
   1. https://adventofcode.com/
   2. https://adventofcode.com/2023/about
   3. https://adventofcode.com/2023/events
   4. https://teespring.com/stores/advent-of-code
   5. https://adventofcode.com/2023/settings
   6. https://adventofcode.com/2023/auth/logout
   7. Advent of Code Supporter
	https://adventofcode.com/2023/support
   8. https://adventofcode.com/2023
   9. https://adventofcode.com/2023
  10. https://adventofcode.com/2023/support
  11. https://adventofcode.com/2023/sponsors
  12. https://adventofcode.com/2023/leaderboard
  13. https://adventofcode.com/2023/stats
  14. https://adventofcode.com/2023/sponsors
  15. https://kotlinlang.org/
  16. https://en.wikipedia.org/wiki/Hot_spring
  17. https://adventofcode.com/2023
  18. https://adventofcode.com/2023/day/10/input
  19. https://twitter.com/intent/tweet?text=I%27ve+completed+%22Pipe+Maze%22+%2D+Day+10+%2D+Advent+of+Code+2023&url=https%3A%2F%2Fadventofcode%2Ecom%2F2023%2Fday%2F10&related=ericwastl&hashtags=AdventOfCode
  20. javascript:void(0);