Day 21.

src/21.rkt

@@ -0,0 +1,47 @@
+#lang racket
+
+(require "../lib.rkt"
+         "IntCode.rkt")
+
+(define input
+  (string->program (car (problem-input 21))))
+
+(define (asciis->integers asciis)
+  (map char->integer
+       (string->list
+        (string-append
+         (string-join asciis "\n") "\n"))))
+
+(define (integers->asciis ints)
+  (list->string (map integer->char ints)))
+
+;; !(A ∧ B ∧ C) ∧ D
+;; Jump if any of the next three tiles are holes
+;; and the fourth tile is ground.
+(define part1
+  (let ([springscript '("OR A J"
+                        "AND B J"
+                        "AND C J"
+                        "NOT J J"
+                        "AND D J"
+                        "WALK")])
+    (last (resume-with-io (exec input) (asciis->integers springscript)))))
+
+;; !(A ∧ B ∧ C) ∧ D ∧ (E ∨ H)
+;; Jump if any of the next three tiles are holes (A, B, C),
+;; but only if the fourth tile is ground (D),
+;; and there is another tile to reach after that,
+;; either by running (E) or by jumping (H)
+(define part2
+  (let ([springscript '("OR A J"
+                        "AND B J"
+                        "AND C J"
+                        "NOT J J"
+                        "AND D J"
+                        "OR E T"
+                        "OR H T"
+                        "AND T J"
+                        "RUN")])
+    (last (resume-with-io (exec input) (asciis->integers springscript)))))
+
+(show-solution part1 part2)