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47 lines
1.7 KiB
Markdown
47 lines
1.7 KiB
Markdown
3 years ago
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https://adventofcode.com/2021/day/9
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## \--- Day 9: Smoke Basin ---
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These caves seem to be [lava tubes](https://en.wikipedia.org/wiki/Lava_tube).
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Parts are even still volcanically active; small hydrothermal vents release
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smoke into the caves that slowly settles like rain.
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If you can model how the smoke flows through the caves, you might be able to
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avoid it and be that much safer. The submarine generates a heightmap of the
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floor of the nearby caves for you (your puzzle input).
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Smoke flows to the lowest point of the area it's in. For example, consider the
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following heightmap:
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[code]
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2 _1_ 9994321 _0_
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3987894921
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98 _5_ 6789892
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8767896789
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989996 _5_ 678
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[/code]
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Each number corresponds to the height of a particular location, where `9` is
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the highest and `0` is the lowest a location can be.
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Your first goal is to find the _low points_ \- the locations that are lower
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than any of its adjacent locations. Most locations have four adjacent
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locations (up, down, left, and right); locations on the edge or corner of the
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map have three or two adjacent locations, respectively. (Diagonal locations do
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not count as adjacent.)
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In the above example, there are _four_ low points, all highlighted: two are in
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the first row (a `1` and a `0`), one is in the third row (a `5`), and one is
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in the bottom row (also a `5`). All other locations on the heightmap have some
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lower adjacent location, and so are not low points.
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The _risk level_ of a low point is _1 plus its height_. In the above example,
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the risk levels of the low points are `2`, `1`, `6`, and `6`. The sum of the
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risk levels of all low points in the heightmap is therefore `_15_`.
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Find all of the low points on your heightmap. _What is the sum of the risk
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levels of all low points on your heightmap?_
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