d06

2019/06.rkt

@@ -0,0 +1,22 @@
+#lang br
+(require racket/file rackunit graph)
+
+(define (string->orbits str)
+  (for/list ([ln (in-list (string-split str))])
+    (map string->symbol (string-split ln ")"))))
+
+(define orbit-recs (string->orbits (file->string "06.rktd")))
+
+(define (count-orbits orbit-recs)
+  (match/values (bfs (undirected-graph orbit-recs) 'COM)
+                [(dists _) (apply + (hash-values dists))]))
+
+;; 1
+(check-eq? (count-orbits orbit-recs) 261306)
+
+(define (count-transfers orbit-recs)
+  (match/values (bellman-ford (undirected-graph orbit-recs) 'YOU)
+                [(dists _) (- (hash-ref dists 'SAN) 2)]))
+
+;; 2
+(check-eq? (count-transfers orbit-recs) 382)