257 lines
11 KiB
Plaintext
257 lines
11 KiB
Plaintext
Advent of Code
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--- Day 20: Donut Maze ---
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You notice a strange pattern on the surface of Pluto and land nearby to get a closer look. Upon closer inspection, you
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realize you've come across one of the famous space-warping mazes of the long-lost Pluto civilization!
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Because there isn't much space on Pluto, the civilization that used to live here thrived by inventing a method for folding
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spacetime. Although the technology is no longer understood, mazes like this one provide a small glimpse into the daily life
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of an ancient Pluto citizen.
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This maze is shaped like a donut. Portals along the inner and outer edge of the donut can instantly teleport you from one
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side to the other. For example:
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A
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A
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#######.#########
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#######.........#
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#######.#######.#
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#######.#######.#
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#######.#######.#
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##### B ###.#
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BC...## C ###.#
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##.## ###.#
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##...DE F ###.#
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##### G ###.#
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#########.#####.#
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DE..#######...###.#
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#.#########.###.#
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FG..#########.....#
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###########.#####
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Z
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Z
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This map of the maze shows solid walls (#) and open passages (.). Every maze on Pluto has a start (the open tile next to AA)
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and an end (the open tile next to ZZ). Mazes on Pluto also have portals; this maze has three pairs of portals: BC, DE, and
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FG. When on an open tile next to one of these labels, a single step can take you to the other tile with the same label. (You
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can only walk on . tiles; labels and empty space are not traversable.)
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One path through the maze doesn't require any portals. Starting at AA, you could go down 1, right 8, down 12, left 4, and
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down 1 to reach ZZ, a total of 26 steps.
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However, there is a shorter path: You could walk from AA to the inner BC portal (4 steps), warp to the outer BC portal (1
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step), walk to the inner DE (6 steps), warp to the outer DE (1 step), walk to the outer FG (4 steps), warp to the inner FG (1
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step), and finally walk to ZZ (6 steps). In total, this is only 23 steps.
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Here is a larger example:
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A
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A
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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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#.....# A C #.#.#.#
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####### S P #####.#
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#.#...# #......VT
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#.#.#.# #.#####
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#...#.# YN....#.#
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#.###.# #####.#
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DI....#.# #.....#
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#####.# #.###.#
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ZZ......# QG....#..AS
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###.### #######
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JO..#.#.# #.....#
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#.#.#.# ###.#.#
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#...#..DI BU....#..LF
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#####.# #.#####
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YN......# VT..#....QG
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#.###.# #.###.#
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#.#...# #.....#
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###.### J L J #.#.###
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#.....# O F P #.#...#
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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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B J C
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U P P
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Here, AA has no direct path to ZZ, but it does connect to AS and CP. By passing through AS, QG, BU, and JO, you can reach ZZ
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in 58 steps.
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In your maze, how many steps does it take to get from the open tile marked AA to the open tile marked ZZ?
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Your puzzle answer was 552.
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--- Part Two ---
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Strangely, the exit isn't open when you reach it. Then, you remember: the ancient Plutonians were famous for building
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recursive spaces.
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The marked connections in the maze aren't portals: they physically connect to a larger or smaller copy of the maze.
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Specifically, the labeled tiles around the inside edge actually connect to a smaller copy of the same maze, and the smaller
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copy's inner labeled tiles connect to yet a smaller copy, and so on.
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When you enter the maze, you are at the outermost level; when at the outermost level, only the outer labels AA and ZZ
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function (as the start and end, respectively); all other outer labeled tiles are effectively walls. At any other level, AA
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and ZZ count as walls, but the other outer labeled tiles bring you one level outward.
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Your goal is to find a path through the maze that brings you back to ZZ at the outermost level of the maze.
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In the first example above, the shortest path is now the loop around the right side. If the starting level is 0, then taking
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the previously-shortest path would pass through BC (to level 1), DE (to level 2), and FG (back to level 1). Because this is
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not the outermost level, ZZ is a wall, and the only option is to go back around to BC, which would only send you even deeper
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into the recursive maze.
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In the second example above, there is no path that brings you to ZZ at the outermost level.
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Here is a more interesting example:
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Z L X W C
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Z P Q B K
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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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#...#.# F R I Z #.#.#.#
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#.###.# D E C H #.#.#.#
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#.#...# #...#.#
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#.###.# #.###.#
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#.#....OA WB..#.#..ZH
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#.###.# #.#.#.#
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CJ......# #.....#
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####### #######
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#.#....CK #......IC
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#.###.# #.###.#
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#.....# #...#.#
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###.### #.#.#.#
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XF....#.# RF..#.#.#
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#####.# #######
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#......CJ NM..#...#
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###.#.# #.###.#
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RE....#.# #......RF
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###.### X X L #.#.#.#
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#.....# F Q P #.#.#.#
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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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A O F N
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A A D M
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One shortest path through the maze is the following:
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• Walk from AA to XF (16 steps)
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• Recurse into level 1 through XF (1 step)
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• Walk from XF to CK (10 steps)
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• Recurse into level 2 through CK (1 step)
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• Walk from CK to ZH (14 steps)
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• Recurse into level 3 through ZH (1 step)
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• Walk from ZH to WB (10 steps)
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• Recurse into level 4 through WB (1 step)
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• Walk from WB to IC (10 steps)
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• Recurse into level 5 through IC (1 step)
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• Walk from IC to RF (10 steps)
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• Recurse into level 6 through RF (1 step)
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• Walk from RF to NM (8 steps)
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• Recurse into level 7 through NM (1 step)
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• Walk from NM to LP (12 steps)
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• Recurse into level 8 through LP (1 step)
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• Walk from LP to FD (24 steps)
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• Recurse into level 9 through FD (1 step)
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• Walk from FD to XQ (8 steps)
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• Recurse into level 10 through XQ (1 step)
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• Walk from XQ to WB (4 steps)
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• Return to level 9 through WB (1 step)
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• Walk from WB to ZH (10 steps)
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• Return to level 8 through ZH (1 step)
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• Walk from ZH to CK (14 steps)
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• Return to level 7 through CK (1 step)
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• Walk from CK to XF (10 steps)
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• Return to level 6 through XF (1 step)
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• Walk from XF to OA (14 steps)
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• Return to level 5 through OA (1 step)
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• Walk from OA to CJ (8 steps)
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• Return to level 4 through CJ (1 step)
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• Walk from CJ to RE (8 steps)
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• Return to level 3 through RE (1 step)
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• Walk from RE to IC (4 steps)
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• Recurse into level 4 through IC (1 step)
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• Walk from IC to RF (10 steps)
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• Recurse into level 5 through RF (1 step)
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• Walk from RF to NM (8 steps)
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• Recurse into level 6 through NM (1 step)
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• Walk from NM to LP (12 steps)
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• Recurse into level 7 through LP (1 step)
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• Walk from LP to FD (24 steps)
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• Recurse into level 8 through FD (1 step)
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• Walk from FD to XQ (8 steps)
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• Recurse into level 9 through XQ (1 step)
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• Walk from XQ to WB (4 steps)
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• Return to level 8 through WB (1 step)
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• Walk from WB to ZH (10 steps)
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• Return to level 7 through ZH (1 step)
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• Walk from ZH to CK (14 steps)
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• Return to level 6 through CK (1 step)
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• Walk from CK to XF (10 steps)
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• Return to level 5 through XF (1 step)
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• Walk from XF to OA (14 steps)
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• Return to level 4 through OA (1 step)
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• Walk from OA to CJ (8 steps)
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• Return to level 3 through CJ (1 step)
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• Walk from CJ to RE (8 steps)
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• Return to level 2 through RE (1 step)
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• Walk from RE to XQ (14 steps)
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• Return to level 1 through XQ (1 step)
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• Walk from XQ to FD (8 steps)
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• Return to level 0 through FD (1 step)
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• Walk from FD to ZZ (18 steps)
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This path takes a total of 396 steps to move from AA at the outermost layer to ZZ at the outermost layer.
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In your maze, when accounting for recursion, how many steps does it take to get from the open tile marked AA to the open tile
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marked ZZ, both at the outermost layer?
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Your puzzle answer was 6492.
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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/Torus
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. https://adventofcode.com/2019
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. https://adventofcode.com/2019/day/20/input
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