commit - d6d76c2348e12e43bf9488048af3427a304053dd
commit + 02ba895db62e5ef212bd779b132e43063548174b
blob - 633c34cadd2a0edac4d06498b8ae0998ac2d6996
blob + 52a7137d9dec7b4dc065906ce37ea2cb695a7ffd
--- src/day-9.lisp
+++ src/day-9.lisp
(:export #:day-9))
(in-package #:aoc/day-9)
-(defun find-next-value (numbers)
- (let ((new-sequence (loop with last = (first numbers)
- for number in (rest numbers)
- collect (- number last)
- do (setf last number))))
- (if (every (curry #'= 0) new-sequence)
- (first numbers)
- (+ (lastcar numbers)
- (find-next-value new-sequence)))))
-
(defun day-9 (input)
- (loop for line = (read-line input nil)
+ (loop with task-1 fixnum = 0
+ with task-2 fixnum = 0
+ for line = (read-line input nil)
while line
for numbers = (read-number-list line)
- sum (find-next-value numbers) into task-1 fixnum
- sum (find-next-value (nreverse numbers)) into task-2 fixnum
+ do (loop with sequences = (list (cons (car numbers)
+ (lastcar numbers)))
+ with current = numbers
+ with current-last = 0
+ for non-zero? = nil
+ do (setf current
+ (loop with last fixnum = (first current)
+ for number fixnum in (rest current)
+ for n = (the fixnum (- number last))
+ unless (xor non-zero?
+ (zerop n))
+ do (setf non-zero? t)
+ collect n
+ do (setf last number)
+ finally (setf current-last n)))
+ do (push (cons (car current)
+ current-last)
+ sequences)
+ while non-zero?
+ finally (progn
+ (loop with next-1 fixnum = 0
+ with next-2 fixnum = 0
+ for current in (rest sequences)
+ do (setf next-1 (+ (the fixnum (cdr current)) next-1)
+ next-2 (- (the fixnum (car current)) next-2))
+ finally (progn
+ (incf task-1 next-1)
+ (incf task-2 next-2)))))
finally (return (values task-1 task-2))))
