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day 7: cleaned up version using graph-lib 

this was a pain in the ass to write vs the initial implementation, but
it's a lot more efficient due to not revisiting nodes that are already
visited. i would warrant it's as efficient as possible at this point

also, both part1 and part2 use the generalized do-dfs form provided by
the graph package
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xenia 2020-12-07 02:35:26 -05:00
parent 69f78e5e6d
commit bcce377a7d
1 changed files with 49 additions and 29 deletions
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7.rkt
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@ -4,48 +4,68 @@
;; solution for day 7 ;; solution for day 7
(define (part1 adjlist all-colors wanted) (define (part1 G wanted)
(define (dfs src dest) (define-vertex-property G has-wanted #:init #f)
(for/or ([item (in-list (hash-ref adjlist src '()))]) (do-dfs G
(or (dfs (car item) dest) (string=? (car item) dest)))) ;; only visit when the to vertex is not already marked with has-wanted
#:visit?: (if (and $from (has-wanted $to))
(begin (has-wanted-set! $from #t) #f)
#t)
;; propagate has-wanted if the child has it
#:epilogue: (when (and $from (or (has-wanted $to) (string=? wanted $to)))
(has-wanted-set! $from #t)))
;; count the results
(for/sum ([(_ v) (in-hash (has-wanted->hash))] #:when v) 1))
;; bad solution (define (part2 G wanted)
(for/sum ([src (in-set all-colors)]) ;; initially, each vertex just counts the weight of itself, which is 1
(if (dfs src wanted) 1 0))) (define-vertex-property G all-weight #:init 1)
(define (part2 adjlist all-colors wanted) ;; accumulates the result in the vertex property tracking all weights
(define (part2-impl src) ;; adds the total weight of $to multiplied by the edge weight of $from -> $to to the total weight
(add1 ;; of $from
(for/sum ([subbag (in-list (hash-ref adjlist src '()))]) ;; this will be called for each neighbor of $from, and $from's total weight starts at 1
(* (cdr subbag) (part2-impl (car subbag)))))) (define (increment $from $to)
(sub1 (part2-impl wanted))) (when $from
(all-weight-set! $from
(+ (all-weight $from)
(* (edge-weight G $from $to) (all-weight $to))))))
(do-dfs G
#:order (lambda (_) (list wanted))
;; always check already-visited nodes
#:process-unvisited?: #t
;; add already-visited nodes to the total
#:process-unvisited: (increment $from $to)
;; add nodes we finished visiting to the total
#:epilogue: (increment $from $to))
;; subtract 1 because we counted the shiny gold bag itself, when we only need the weight of
;; what's inside it
(sub1 (all-weight wanted)))
(module+ main (module+ main
(define input (file->lines "inputs/7")) (define input-lines (file->lines "inputs/7"))
(define all-colors (mutable-set)) (define edges
(define adjlist (apply append
(for/hash ([line (in-list input)]) (for/list ([line (in-list input-lines)])
(match line (match line
[(pregexp #px"^([a-z ]+) bags contain ([^\\.]+).$" (list _ src-color contains)) [(pregexp #px"^([a-z ]+) bags contain ([^\\.]+).$" (list _ src-color contains))
(set-add! all-colors src-color)
(values src-color
(if (string=? "no other bags" contains) (if (string=? "no other bags" contains)
'() '()
(for/list ([item (in-list (string-split contains ", "))]) (for/list ([item (in-list (string-split contains ", "))])
(match item (match item
[(pregexp #px"^([0-9]+) ([a-z ]+) bag[s]?" [(pregexp #px"^([0-9]+) ([a-z ]+) bag[s]?"
(list _ (app string->number number) color)) (list _ (app string->number number) dst-color))
(set-add! all-colors color) (list number src-color dst-color)]
(cons color number)] [x (error "not shonks" x)])))]
[x (error "not shonks" x)]))))] [x (error "not shonks" x)]))))
[x (error "not shonks" x)]))) (define input (weighted-graph/directed edges))
(define wanted "shiny gold") (define wanted "shiny gold")
;; part 1 ;; part 1
(answer 7 1 (part1 adjlist all-colors wanted)) (answer 7 1 (part1 input wanted))
;; part 2 ;; part 2
(answer 7 2 (part2 adjlist all-colors wanted)) (answer 7 2 (part2 input wanted))
(displayln "meow")) (displayln "meow"))