Racket solutions & explanations for the Advent of Code puzzles
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aoc-racket/day08.rkt

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#lang scribble/lp2
@(require scribble/manual aoc-racket/helper)
@aoc-title[8]
@defmodule[aoc-racket/day08]
@link["http://adventofcode.com/day/8"]{The puzzle}. Our @link-rp["day08-input.txt"]{input} consists of a list of seemingly random strings within quotation marks.
@chunk[<day08>
<day08-setup>
<day08-q1>
<day08-q2>
<day08-test>]
@isection{What's the difference between the literal length of the strings, and their length in memory?}
The puzzle relies the fact that within strings, certain single characters  like the backslash @litchar{\} and double-quote mark @litchar{"} — are described with more than one character. Thus, the question asks us to compare the two lengths.
The literal length of the string is trivial — use @iracket[string-length]. The memory length requires interpreting a string as a Racket value, which (as seen in @secref{Day_7}) simply means using @iracket[read].
@chunk[<day08-setup>
(require racket rackunit)
(provide (all-defined-out))
]
@chunk[<day08-q1>
(define (memory-length str) (string-length (read (open-input-string str))))
(define (q1 strs)
(- (apply + (map string-length strs)) (apply + (map memory-length strs))))]
@isection{What's the difference between the re-encoded length of the literal string, and the original length?}
This question simply comes down to — do you know how to use the string-formatting functions in your programming language?
In Racket, a string can be re-encoded with @iracket[~v]. Not a very puzzling puzzle overall.
@chunk[<day08-q2>
(define (encoded-length str) (string-length (~v str)))
(define (q2 strs)
(- (apply + (map encoded-length strs)) (apply + (map string-length strs)))) ]
@section{Testing Day 8}
@chunk[<day08-test>
(module+ test
(define input-strs (file->lines "day08-input.txt"))
(check-equal? (q1 input-strs) 1333)
(check-equal? (q2 input-strs) 2046))]