From bcce377a7dec35c1fed4d9b868fe5ef9f6ab0098 Mon Sep 17 00:00:00 2001
From: haskal <haskal@awoo.systems>
Date: Mon, 7 Dec 2020 02:35:26 -0500
Subject: [PATCH] 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
---
 7.rkt | 78 +++++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 49 insertions(+), 29 deletions(-)

diff --git a/7.rkt b/7.rkt
index dcf7c22..8881a9f 100644
--- a/7.rkt
+++ b/7.rkt
@@ -4,48 +4,68 @@
 
 ;; solution for day 7
 
-(define (part1 adjlist all-colors wanted)
-  (define (dfs src dest)
-    (for/or ([item (in-list (hash-ref adjlist src '()))])
-      (or (dfs (car item) dest) (string=? (car item) dest))))
+(define (part1 G wanted)
+  (define-vertex-property G has-wanted #:init #f)
+  (do-dfs G
+    ;; 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
-  (for/sum ([src (in-set all-colors)])
-    (if (dfs src wanted) 1 0)))
+(define (part2 G wanted)
+  ;; initially, each vertex just counts the weight of itself, which is 1
+  (define-vertex-property G all-weight #:init 1)
 
-(define (part2 adjlist all-colors wanted)
-  (define (part2-impl src)
-    (add1
-      (for/sum ([subbag (in-list (hash-ref adjlist src '()))])
-        (* (cdr subbag) (part2-impl (car subbag))))))
-  (sub1 (part2-impl wanted)))
+  ;; accumulates the result in the vertex property tracking all weights
+  ;; adds the total weight of $to multiplied by the edge weight of $from -> $to to the total weight
+  ;; of $from
+  ;; this will be called for each neighbor of $from, and $from's total weight starts at 1
+  (define (increment $from $to)
+    (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
-  (define input (file->lines "inputs/7"))
-  (define all-colors (mutable-set))
-  (define adjlist
-    (for/hash ([line (in-list input)])
-      (match line
-        [(pregexp #px"^([a-z ]+) bags contain ([^\\.]+).$" (list _ src-color contains))
-         (set-add! all-colors src-color)
-         (values src-color
+  (define input-lines (file->lines "inputs/7"))
+  (define edges
+    (apply append
+           (for/list ([line (in-list input-lines)])
+             (match line
+               [(pregexp #px"^([a-z ]+) bags contain ([^\\.]+).$" (list _ src-color contains))
                  (if (string=? "no other bags" contains)
                    '()
                    (for/list ([item (in-list (string-split contains ", "))])
                      (match item
                        [(pregexp #px"^([0-9]+) ([a-z ]+) bag[s]?"
-                                 (list _ (app string->number number) color))
-                        (set-add! all-colors color)
-                        (cons color number)]
-                       [x (error "not shonks" x)]))))]
-        [x (error "not shonks" x)])))
-
+                                 (list _ (app string->number number) dst-color))
+                        (list number src-color dst-color)]
+                       [x (error "not shonks" x)])))]
+               [x (error "not shonks" x)]))))
+  (define input (weighted-graph/directed edges))
   (define wanted "shiny gold")
 
   ;; part 1
-  (answer 7 1 (part1 adjlist all-colors wanted))
+  (answer 7 1 (part1 input wanted))
 
   ;; part 2
-  (answer 7 2 (part2 adjlist all-colors wanted))
+  (answer 7 2 (part2 input wanted))
 
   (displayln "meow"))