commit - 8c78fb5cb90087550a894bd7d8d992922ece70ce
commit + c3dffd28b9750ff8439ddddc5b5fece451000406
blob - bcc3db7b442e9a4367a2a8d1b32fb5b4c8ea3f37
blob + e574fbee0d27fc9b3e571e6da44319facd7ead6a
--- src/day-20.lisp
+++ src/day-20.lisp
modules))
(defun day-20 (input)
- (let* ((modules (parse-input input))
- (broadcast (gethash "broadcaster" modules)))
- (loop with low-count = 0
- with high-count = 0
- repeat 1000
- do (loop with next = (list (list nil broadcast :low))
- while next
- for next-next = (loop for (from to type) in next
- do (ecase type
- (:low (incf low-count))
- (:high (incf high-count)))
- nconc (pulse to from type))
- do (setf next next-next))
- finally (return (* low-count high-count)))))
+ (loop with modules = (parse-input input)
+ with broadcast = (gethash "broadcaster" modules)
+ with rx-source-modules = (when-let (rx (gethash "rx" modules))
+ (module-connected (first (module-connected rx))))
+ with rx-source-intervals = (make-hash-table)
+ with task-1 = 0
+ with task-2 = 0
+ with low-count = 0
+ with high-count = 0
+ for i from 1
+ do (loop with next = (list (list nil broadcast :low))
+ while next
+ for n = (loop for (from to type) in next
+ do (ecase type
+ (:low (incf low-count))
+ (:high (progn
+ (when (and (member from rx-source-modules)
+ (not (gethash from rx-source-intervals)))
+ (setf (gethash from rx-source-intervals) i))
+ (incf high-count))))
+ nconc (pulse to from type))
+ do (setf next n))
+ when (= i 1000)
+ do (setf task-1 (* low-count high-count))
+ when (= (hash-table-count rx-source-intervals) (length rx-source-modules))
+ do (setf task-2 (apply #'lcm (hash-table-values rx-source-intervals)))
+ when (if rx-source-modules (> task-2 0) (> task-1 0))
+ do (return (values task-1 task-2))))
