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diff --git a/perfectly-spherical-houses-in-a-vacuum/README.org b/perfectly-spherical-houses-in-a-vacuum/README.org new file mode 100644 index 0000000..39fd3d6 --- /dev/null +++ b/perfectly-spherical-houses-in-a-vacuum/README.org @@ -0,0 +1,41 @@ +See: https://adventofcode.com/2015/day/3 +** Part 1 +*** Purpose +Given a list of directional arrows: + +#+begin_example +^>><v +#+end_example + +Determine how many unique spaces on a grid are reached. + +*** Method + +As a more creative solution, we can use closure to create an environment which keeps track of visited spaces. Say this environment contains an initial variable with this value: + +#+begin_example +'((0 . 0)) +#+end_example + +And we translate each instruction to a different pair of values, each representing a direction. + +^>><v: + +#+begin_example +'((0 . 1) + (1 . 0) + (1 . 0) + (-1 . 0) + (0 . -1)) +#+end_example + +Then simply call the procedure that is encapsulated by a local environment, and have it add the cons pair to the previous and update its internal state. + +Finally, we can have another procedure that returns the length of the local list. + +** Part 2 +*** Purpose +The next part claims we now have two visitors. Each of them take turns receiving directions. I chose an object-like approach for part one because the original problem claimed we were tracking "Santa" visiting houses---this is a good thing, which truly shines now that we have two visitors. + +*** Method +All we need to do is change the main function to create multiple visitors, store them in a list, and cycle through the list of visitors when we process instructions. |