73 lines
2.7 KiB
Markdown
Executable File
73 lines
2.7 KiB
Markdown
Executable File
## \-\-\- Day 23: A Long Walk ---
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The Elves resume water filtering operations! Clean water starts flowing over the edge of Island Island.
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They offer to help _you_ go over the edge of Island Island, too! Just hold on tight to one end of this impossibly long rope and they'll lower you down a safe distance from the massive waterfall you just created.
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As you finally reach Snow Island, you see that the water isn't really reaching the ground: it's being _absorbed by the air_ itself. It looks like you'll finally have a little downtime while the moisture builds up to snow-producing levels. Snow Island is pretty scenic, even without any snow; why not take a walk?
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There's a map of nearby hiking trails (your puzzle input) that indicates _paths_ ( `.`), _forest_ ( `#`), and steep _slopes_ ( `^`, `>`, `v`, and `<`).
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For example:
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```
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#.#####################
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#.......#########...###
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#######.#########.#.###
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###.....#.>.>.###.#.###
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###v#####.#v#.###.#.###
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###.>...#.#.#.....#...#
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###v###.#.#.#########.#
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###...#.#.#.......#...#
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#####.#.#.#######.#.###
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#.....#.#.#.......#...#
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#.#####.#.#.#########v#
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#.#...#...#...###...>.#
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#.#.#v#######v###.###v#
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#...#.>.#...>.>.#.###.#
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#####v#.#.###v#.#.###.#
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#.....#...#...#.#.#...#
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#.#########.###.#.#.###
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#...###...#...#...#.###
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###.###.#.###v#####v###
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#...#...#.#.>.>.#.>.###
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#.###.###.#.###.#.#v###
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#.....###...###...#...#
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#####################.#
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```
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You're currently on the single path tile in the top row; your goal is to reach the single path tile in the bottom row. Because of all the mist from the waterfall, the slopes are probably quite _icy_; if you step onto a slope tile, your next step must be _downhill_ (in the direction the arrow is pointing). To make sure you have the most scenic hike possible, _never step onto the same tile twice_. What is the longest hike you can take?
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In the example above, the longest hike you can take is marked with `O`, and your starting position is marked `S`:
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```
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#S#####################
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#OOOOOOO#########...###
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#######O#########.#.###
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###OOOOO#OOO>.###.#.###
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###O#####O#O#.###.#.###
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###OOOOO#O#O#.....#...#
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###v###O#O#O#########.#
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###...#O#O#OOOOOOO#...#
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#####.#O#O#######O#.###
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#.....#O#O#OOOOOOO#...#
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#.#####O#O#O#########v#
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#.#...#OOO#OOO###OOOOO#
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#.#.#v#######O###O###O#
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#...#.>.#...>OOO#O###O#
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#####v#.#.###v#O#O###O#
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#.....#...#...#O#O#OOO#
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#.#########.###O#O#O###
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#...###...#...#OOO#O###
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###.###.#.###v#####O###
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#...#...#.#.>.>.#.>O###
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#.###.###.#.###.#.#O###
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#.....###...###...#OOO#
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#####################O#
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```
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This hike contains `94` steps. (The other possible hikes you could have taken were `90`, `86`, `82`, `82`, and `74` steps long.)
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Find the longest hike you can take through the hiking trails listed on your map. _How many steps long is the longest hike?_ |