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#lang scribble/lp2
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@(require scribble/manual aoc-racket/helper)
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@aoc-title[12]
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@defmodule[aoc-racket/day12]
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@link["http://adventofcode.com/day/12"]{The puzzle}. Our @link-rp["day12-input.txt"]{input} is, unfortunately, a @link["http://json.org/"]{JSON} file.
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@chunk[<day12>
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<day12-setup>
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<day12-q1>
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<day12-q2>
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<day12-test>]
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@isection{What's the sum of all the numbers in the document?}
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I've never liked JavaScript, and spending more time with Racket has only deepened my antipathy. So I apologize if this solution is terse.
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We need to parse the JSON file, extract the numbers, and add them.
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To parse the file we'll use the @iracket[read-json] function from Racket's @racketmodname[json] library. This function converts the JSON into a JS-expression (see @iracket[jsexpr?]), which is a recursively nested data structure. If we had a simple recursively nested list, we could just @iracket[flatten] it and filter for the numbers. We'll do something similar here — recursively flatten the JS-expression and pull out the numbers.
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If you're new to Racket, notice the @italic{recursive descent} pattern used in @racket[flatten-jsexpr] — it's a very common way of handling recursively structured data.
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@chunk[<day12-setup>
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(require racket rackunit json)
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(provide (all-defined-out))
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(define (string->jsexpr str)
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(read-json (open-input-string str)))
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]
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@chunk[<day12-q1>
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(define (flatten-jsexpr jsexpr)
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(flatten
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(let loop ([x jsexpr])
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(cond
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[(list? x)
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(map loop x)]
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[(hash? x)
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(loop (flatten (hash->list x)))]
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[else x]))))
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(define (q1 input-str)
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(define json-items (flatten-jsexpr (string->jsexpr input-str)))
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(apply + (filter number? json-items)))]
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@section{What's the sum of all the numbers, if hash tables with value @racket{red} are ignored?}
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We'll just update our flattening function to skip over hash tables that have @racket{red} among the values.
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@chunk[<day12-q2>
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(define (flatten-jsexpr-2 jsexpr)
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(flatten
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(let loop ([x jsexpr])
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(cond
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[(list? x)
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(map loop x)]
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[(hash? x)
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(if (member "red" (hash-values x))
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empty
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(loop (flatten (hash->list x))))]
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[else x]))))
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(define (q2 input-str)
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(define json-items (flatten-jsexpr-2 (string->jsexpr input-str)))
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(apply + (filter number? json-items))) ]
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@section{Testing Day 12}
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@chunk[<day12-test>
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(module+ test
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(define input-str (file->string "day12-input.txt"))
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(check-equal? (q1 input-str) 191164)
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(check-equal? (q2 input-str) 87842))]
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