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68 lines
2.5 KiB
68 lines
2.5 KiB
#lang scribble/lp2


@(require scribble/manual aocracket/helper)




@aoctitle[2]




@defmodule[aocracket/day02]




@link["http://adventofcode.com/day/2"]{The puzzle}. Our @linkrp["day02input.txt"]{input} is a list of strings that represent dimensions of rectangular boxes.




@chunk[<day02>


<day02setup>


<day02q1>


<day02test>]






@isection{How much paper is needed to wrap the boxes?}




According to the problem, the paper needed to wrap a present is the surface area of the box (= the sum of the areas of the sides) plus the area of the smallest side.




First we need to parse our input file into a list of box dimensions. We'll model each box as a list of three dimensions. (The question doesn't need us to keep height / width / depth straight, so we won't worry about it.)




Then we have a traditional setup for the devastating onetwo punch of @iracket[map] and @iracket[apply]. We'll write a function to compute surface area from box dimensions. Then we'll @racket[map] that function across the list of boxes, and finally @racket[apply] the @racket[+] operator to our list of results to get the answer.






@chunk[<day02setup>


(require racket rackunit)


(provide (alldefinedout))


(define (string>boxes str)


(for/list ([ln (inlist (stringsplit str "\n"))])


(map string>number (stringsplit ln "x"))))]




@chunk[<day02q1>


(define (box>paper box)


(matchdefine (list x y z) box)


(define sides (list (* x y) (* y z) (* x z)))


(+ (* 2 (apply + sides)) (apply min sides)))




(define (q1 str)


(define boxes (string>boxes str))


(apply + (map box>paper boxes)))]




@section{How much ribbon is needed to wrap the boxes?}




According to the problem, the ribbon needed is the perimeter of the smallest side plus the volume of the box.




We take the same approach, with a new @racket[box>ribbon] function.




@chunk[<day02q1>


(define (box>ribbon box)


(matchdefine (list x y z) box)


(define (perimeter dim1 dim2) (* 2 (+ dim1 dim2)))


(define perimeters


(list (perimeter x y) (perimeter y z) (perimeter x z)))


(+ (apply min perimeters) (* x y z)))




(define (q2 str)


(define boxes (string>boxes str))


(apply + (map box>ribbon boxes)))]






@section{Testing Day 2}






@chunk[<day02test>


(module+ test


(define inputstr (file>string "day02input.txt"))


(checkequal? (q1 inputstr) 1586300)


(checkequal? (q2 inputstr) 3737498))] 