Add day7

Author: opsound

2020/day7.rkt

@@ -0,0 +1,53 @@
+#lang racket
+
+(define LINES (file->lines "day7.txt"))
+
+(struct bag (adjective color) #:transparent)
+
+(define (string-split-normalize s sep)
+  (map string-normalize-spaces (string-split s sep)))
+
+(define (string->words s)
+  (string-split s " "))
+
+(define (string->bag-num s)
+  (let ([words (string->words s)])
+    (cons (apply bag (cdr words))
+          (string->number (car words)))))
+
+(define (string->bags s)
+  (if (string-prefix? s "no")
+      '()
+      (map string->bag-num (string-split s ","))))
+   
+(define (string->rule s)
+  (match-let* ([cleaned (string-replace (string-replace s #rx"bags?" "") "." "")]
+               [(list left right) (string-split-normalize cleaned "contain")]
+               [left-bag (apply bag (string->words left))]
+               [right-bags (string->bags right)])               
+    (list left-bag right-bags)))
+
+(define RULES (apply hash (apply append (map string->rule LINES))))
+
+(define (bag-contains? b c)
+  (let ([bags (hash-ref RULES b)])
+    (if (empty? bags)
+        #f
+        (if (assoc c bags)
+            #t
+            (for/or ([candidate (map car bags)])
+              (bag-contains? candidate c))))))
+
+(count values (map (λ (b) (bag-contains? b (bag "shiny" "gold"))) (hash-keys RULES)))
+
+(define (bag-count b)
+  (let ([bags (hash-ref RULES b)])
+    (if (empty? bags)
+        0
+        (+ (apply + (map cdr bags))
+           (for/fold ([sum 0])
+                     ([candidate (map car bags)]
+                      [count (map cdr bags)])
+             (+ sum (* count (bag-count candidate))))))))
+
+(bag-count (bag "shiny" "gold"))