2022 day 8 init

2022/day08/README.org

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+** --- Day 8: Treetop Tree House ---
+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
+[[https://en.wikipedia.org/wiki/Tree_house][tree house]].
+
+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.
+
+The Elves have already launched a
+[[https://en.wikipedia.org/wiki/Quadcopter][quadcopter]] to generate a
+map with the height of each tree (your puzzle input). For example:
+
+#+begin_example
+30373
+25512
+65332
+33549
+35390
+#+end_example
+
+Each tree is represented as a single digit whose value is its height,
+where =0= is the shortest and =9= is the tallest.
+
+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.
+
+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:
+
+- 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.)
+- The top-middle =5= is /visible/ from the top and right.
+- 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.
+- The left-middle =5= is /visible/, but only from the right.
+- 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.
+- The right-middle =3= is /visible/ from the right.
+- In the bottom row, the middle =5= is /visible/, but the =3= and =4=
+  are not.
+
+With 16 trees visible on the edge and another 5 visible in the interior,
+a total of =21= trees are visible in this arrangement.
+
+Consider your map; /how many trees are visible from outside the grid?/
+
+To begin, [[file:8/input][get your puzzle input]].