2018 day 2 complete

1 files changed, 27 insertions, 0 deletions

diff --git a/aoc2018/day-02/day-02.rkt b/aoc2018/day-02/day-02.rkt
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+++ b/aoc2018/day-02/day-02.rkt
@@ -0,0 +1,27 @@
+#lang racket
+
+(require advent-of-code
+         threading)
+
+(define ids (port->lines (open-aoc-input (find-session) 2018 2 #:cache #true)))
+
+;; part 1
+(define (make-baskets str)
+  (for/fold ([baskets (hash)]) ([ch (in-string str)])
+    (hash-update baskets ch add1 0)))
+
+(define (has-count n ht)
+  (member n (hash-values ht)))
+
+(for/fold ([two 0] [three 0] #:result (* two three)) ([id (in-list ids)])
+  (define baskets (make-baskets id))
+  (values (if (has-count 2 baskets) (add1 two) two) (if (has-count 3 baskets) (add1 three) three)))
+
+;; part 2
+(define (string-difference str1 str2)
+  (for/sum ([ch1 (in-string str1)] [ch2 (in-string str2)]) (if (equal? ch1 ch2) 0 1)))
+
+(for*/first ([id1 (in-list ids)] [id2 (in-list ids)] #:when (= 1 (string-difference id1 id2)))
+  (~>> (for/list ([ch1 (in-string id1)] [ch2 (in-string id2)] #:when (equal? ch1 ch2))
+         ch1)
+       (apply string)))