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39 lines
2.4 KiB
39 lines
2.4 KiB
1 year ago
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# Day 8: Treetop Tree House
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[https://adventofcode.com/2022/day/8](https://adventofcode.com/2022/day/8)
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## Description
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### Part One
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The expedition comes across a peculiar patch of tall trees all planted carefully in a grid. The Elves explain that a previous expedition planted these trees as a reforestation effort. Now, they're curious if this would be a good location for a [tree house](https://en.wikipedia.org/wiki/Tree_house).
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First, determine whether there is enough tree cover here to keep a tree house _hidden_. To do this, you need to count the number of trees that are _visible from outside the grid_ when looking directly along a row or column.
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The Elves have already launched a [quadcopter](https://en.wikipedia.org/wiki/Quadcopter) to generate a map with the height of each tree (<span title="The Elves have already launched a quadcopter (your puzzle input).">your puzzle input</span>). For example:
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30373
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25512
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65332
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33549
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35390
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Each tree is represented as a single digit whose value is its height, where `0` is the shortest and `9` is the tallest.
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A tree is _visible_ if all of the other trees between it and an edge of the grid are _shorter_ than it. Only consider trees in the same row or column; that is, only look up, down, left, or right from any given tree.
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All of the trees around the edge of the grid are _visible_ - since they are already on the edge, there are no trees to block the view. In this example, that only leaves the _interior nine trees_ to consider:
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* The top-left `5` is _visible_ from the left and top. (It isn't visible from the right or bottom since other trees of height `5` are in the way.)
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* The top-middle `5` is _visible_ from the top and right.
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* The top-right `1` is not visible from any direction; for it to be visible, there would need to only be trees of height _0_ between it and an edge.
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* The left-middle `5` is _visible_, but only from the right.
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* The center `3` is not visible from any direction; for it to be visible, there would need to be only trees of at most height `2` between it and an edge.
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* The right-middle `3` is _visible_ from the right.
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* In the bottom row, the middle `5` is _visible_, but the `3` and `4` are not.
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With 16 trees visible on the edge and another 5 visible in the interior, a total of _`21`_ trees are visible in this arrangement.
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Consider your map; _how many trees are visible from outside the grid?_
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