Day 10

input/10.txt

@@ -0,0 +1,138 @@
+noop
+noop
+addx 5
+addx 29
+addx -28
+addx 5
+addx -1
+noop
+noop
+addx 5
+addx 12
+addx -6
+noop
+addx 4
+addx -1
+addx 1
+addx 5
+addx -31
+addx 32
+addx 4
+addx 1
+noop
+addx -38
+addx 5
+addx 2
+addx 3
+addx -2
+addx 2
+noop
+addx 3
+addx 2
+addx 5
+addx 2
+addx 3
+noop
+addx 2
+addx 3
+noop
+addx 2
+addx -32
+addx 33
+addx -20
+addx 27
+addx -39
+addx 1
+noop
+addx 5
+addx 3
+noop
+addx 2
+addx 5
+noop
+noop
+addx -2
+addx 5
+addx 2
+addx -16
+addx 21
+addx -1
+addx 1
+noop
+addx 3
+addx 5
+addx -22
+addx 26
+addx -39
+noop
+addx 5
+addx -2
+addx 2
+addx 5
+addx 2
+addx 23
+noop
+addx -18
+addx 1
+noop
+noop
+addx 2
+noop
+noop
+addx 7
+addx 3
+noop
+addx 2
+addx -27
+addx 28
+addx 5
+addx -11
+addx -27
+noop
+noop
+addx 3
+addx 2
+addx 5
+addx 2
+addx 27
+addx -26
+addx 2
+addx 5
+addx 2
+addx 4
+addx -3
+addx 2
+addx 5
+addx 2
+addx 3
+addx -2
+addx 2
+noop
+addx -33
+noop
+noop
+noop
+noop
+addx 31
+addx -26
+addx 6
+noop
+noop
+addx -1
+noop
+addx 3
+addx 5
+addx 3
+noop
+addx -1
+addx 5
+addx 1
+addx -12
+addx 17
+addx -1
+addx 5
+noop
+noop
+addx 1
+noop
+noop

lib.rkt

@@ -91,6 +91,14 @@
 (define (show-solution part1 part2)
   (printf "Part 1: ~a\nPart 2: ~a\n" part1 part2))
 
+;; show-solution* : (-> a) -> (-> b) -> void
+;; Like show-solution, but parts 1 and 2 are thunks.
+(define (show-solution* part1 part2)
+  (display "Part 1: ")
+  (displayln (part1))
+  (display "Part 2: ")
+  (displayln (part2)))
+
 
 ;; String helpers ;;
 

src/10.rkt

@@ -0,0 +1,49 @@
+#lang curly-fn racket
+
+(require "../lib.rkt")
+
+(define input
+  (map (∘ (match-lambda
+            ['("noop") 'noop]
+            [`("addx" ,n) (list 'addx (string->number n))])
+          #{string-split %1 " "})
+       (problem-input 10)))
+
+(define (part1)
+  (define strengths 0)
+  (define (update! cycle X)
+    (when (zero? (% (- cycle 20) 40))
+      (set! strengths (+ strengths (* cycle X)))))
+  (for/fold ([X 1] [cycle 1]
+             #:result strengths)
+            ([instr input])
+    (match instr
+      ['noop
+       (update! cycle X)
+       (values X (add1 cycle))]
+      [`(addx ,n)
+       (update! cycle X)
+       (update! (add1 cycle) X)
+       (values (+ X n) (+ cycle 2))])))
+
+(define (part2)
+  (define CRT (make-vector 240))
+  (define (update! pos X)
+    (if (<= (sub1 X) (% pos 40) (add1 X))
+        (vector-set! CRT pos #\█)
+        (vector-set! CRT pos #\ )))
+  (for/fold ([X 1] [pos 0])
+            ([instr input])
+    (match instr
+      ['noop
+       (update! pos X)
+       (values X (add1 pos))]
+      [`(addx ,n)
+       (update! pos X)
+       (update! (add1 pos) X)
+       (values (+ X n) (+ pos 2))]))
+  (displayln "See below.")
+  (for ([s (in-slice 40 CRT)])
+    (displayln (list->string s))))
+
+(show-solution* part1 part2)