the tortoise and the pain

day1.rkt

@@ -1,15 +1,31 @@
 #lang racket
 (require "lib/common.rkt")
 
+(define (sum lst) (foldr + 0 lst))
+
 (define (day1a lst)
-  (void))
+  (for/sum ([v (in-list lst)]
+            [next (in-list (rest lst))])
+    (if (< v next) 1 0)))
 
 (define (day1b lst)
-  (void))
+  (define sum-list
+    (let loop ([current-lst lst])
+      (cond [(< (length current-lst) 3) empty]
+            [else (cons (sum (take current-lst 3))
+                        (loop (rest current-lst)))])))
+
+  (day1a sum-list))
 
 (module+ main
   (call-with-input-file "data/day1.txt"
     (lambda (prt)
-      (define lines (port->lines prt))
+      (define lines (map string->number (port->lines prt)))
       (answer 1 1 (day1a lines))
       (answer 1 2 (day1b lines)))))
+
+(module+ test
+  (require rackunit)
+
+  (define lines '(199 200 208 210 200 207 240 269 260 263))
+  (check-equal? (day1b lines) 5))