Racket solutions & explanations for the Advent of Code puzzles
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aoc-racket/2019
Matthew Butterick 3dbf136103 d23 p2 (stuck) 3 years ago
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01.rkt 2019 d01 & d02 3 years ago
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03.rkt simplify loop 3 years ago
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04.rkt use integers 3 years ago
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05.rkt simplify 3 years ago
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06.rkt d06 alternate solution 3 years ago
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07-gen.rkt d07 alternate solution with generators 3 years ago
07.rkt d07 pt2 3 years ago
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09.rkt tidy 3 years ago
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10.rkt rectangularity 3 years ago
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14input.rkt d14 p1 3 years ago
14test.rkt d14 p1 3 years ago
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16.rkt ref 3 years ago
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25.rkt d25 start 3 years ago
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README.md Update README.md 3 years ago

README.md

MB’s Advent of Code tips

  • The problems are often designed around a particular computer-y abstraction. If you notice what the abstraction is, and then find the closest analog in Racket, the solution tends to come together quickly. Otherwise, you can spend a lot of time reinventing the wheel.

  • Complex numbers are a nice way of modeling two-dimensional positions.

  • Use lists whenever feasible, because there are many useful list functions in the Racket library that don’t have vector equivalents. In particular, these list functions are very useful, especially argmin and argmax.

  • Vectors are better than lists in situations where you need random access to members.

  • eq? is the fastest equality check, but it only works for symbols and fixnums (therefore, use more symbols and fixnums so you can use eq?!)

  • match is fantastic.

  • Association lists (= lists of pairs) are underrated. They’re compatible with all the usual list functions, of course, but also dictionary forms (like dict-ref and in-dict).

  • The graph library can be helpful for graph-based problems.

  • It’s good to know about sets and mutable pairs.

  • Also the fancier for iterators, like for/first and for/or.

  • let/ec is a way of jumping out of a deeply nested computation, akin to how return works in other languages.

My solutions

  • I try to write solutions that are succinct but not cryptic.

  • I don’t optimize for speed.

  • I like doing the Advent of Code problems because it forces me to use parts of Racket that I don’t ordinarily use. So I treat it as a chance to expand my awareness of the Racketverse.

  • I’m unlikely to finish every problem. Judging by past years, there is a point where the problems get sufficiently complex that I’d rather put that time into improving my other Racket projects 🤘