@ -16,7 +16,7 @@ Our @link-rp["day6-input.txt"]{input} is a list instructions for turning on (or
We need to a) create a data structure to hold our grid of lights, then b) step through the instructions on the list, and then c) count how many lights are lit at the end.
When you need random access across a fixed-size set of items, you should think @secref["vectors" #:doc '(lib "scribblings/guide/guide.scrbl")]. (We could do this problem with a @seclink["hash-tables" #:doc '(lib "scribblings/guide/guide.scrbl")]{hash table}, but it would be a lot slower.) The grid-ness of the problem might suggest a two-dimensional vector —e.g., a 1000-unit vector where each slot holds another 1000-unit vector. But this doesn't buy us any convenience. We'll just use a single @racket[(* 1000 1000)]-unit vector, and translate our Cartesian coordinates into linear vector indexes by treating a coordinate like @tt{(246,139)} as @racket[246139].
When you need random access to a fixed-size set of items, you should think @secref["vectors" #:doc '(lib "scribblings/guide/guide.scrbl")]. (We could do this problem with a @seclink["hash-tables" #:doc '(lib "scribblings/guide/guide.scrbl")]{hash table}, but it would be a lot slower.) The grid-ness of the problem might suggest a two-dimensional vector —e.g., a 1000-unit vector where each slot holds another 1000-unit vector. But this doesn't buy us any convenience. We'll just use a single @racket[(* 1000 1000)]-unit vector, and translate our Cartesian coordinates into linear vector indexes by treating a coordinate like @tt{(246,139)} as @racket[246139].
Each instruction consists of two pieces. First, an operation:either @italic{turn on}, @italic{turn off}, or @italic{toggle} (meaning, invert the current state of the bulb). Second, a definition of a rectangular segment of the grid that the operation will be applied to (e.g., @italic{333,60 through 748,159}). Therefore, a natural way to model each instruction is as a Racket function followed by four numerical arguments.
