From ea936e0a78223c02d6e56954c60cf4a29b5e2983 Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Thu, 10 Dec 2020 13:50:08 +0100 Subject: feat(tazjin/aoc2020): Add solution for day 8, part 2 Change-Id: I03f46faf9b5b1b578b1131ecd08746f1adc3e87f Reviewed-on: https://cl.tvl.fyi/c/depot/+/2243 Reviewed-by: tazjin Tested-by: BuildkiteCI --- users/tazjin/aoc2020/solution-day8.el | 58 ++++++++++++++++++++++++++--------- 1 file changed, 44 insertions(+), 14 deletions(-) (limited to 'users') diff --git a/users/tazjin/aoc2020/solution-day8.el b/users/tazjin/aoc2020/solution-day8.el index eb84badde398..591a07fbf3a0 100644 --- a/users/tazjin/aoc2020/solution-day8.el +++ b/users/tazjin/aoc2020/solution-day8.el @@ -13,21 +13,51 @@ (s-lines (s-chomp (f-read "/tmp/aoc/day8.txt")))))) (defun day8/step (code position acc) - (let ((current (aref code position))) - (aset code position nil) - (pcase current - ('() (cons 'final acc)) - (`(nop . ,val) (cons (+ position 1) acc)) - (`(acc . ,val) (cons (+ position 1) (+ acc val))) - (`(jmp . ,val) (cons (+ position val) acc))))) + (if (>= position (length code)) + (cons 'final acc) + + (let ((current (aref code position))) + (aset code position :done) + (pcase current + (:done (cons 'loop acc)) + (`(nop . ,val) (cons (+ position 1) acc)) + (`(acc . ,val) (cons (+ position 1) (+ acc val))) + (`(jmp . ,val) (cons (+ position val) acc)))))) ;; Puzzle 1 (message "Solution to day8/1: %s" - (let ((code (copy-sequence day8/input)) - (position 0) - (acc 0)) - (cl-loop for next = (day8/step code position acc) - when (equal 'final (car next)) return (cdr next) - do (setq position (car next)) - do (setq acc (cdr next))))) + (let ((code (copy-sequence day8/input)) + (position 0) + (acc 0)) + (cl-loop for next = (day8/step code position acc) + when (equal 'loop (car next)) return (cdr next) + do (setq position (car next)) + do (setq acc (cdr next))))) + +;; Puzzle 2 + +(defun day8/flip-at (code pos) + (pcase (aref code pos) + (`(nop . ,val) (aset code pos `(jmp . ,val))) + (`(jmp . ,val) (aset code pos `(nop . ,val))) + (other (error "Unexpected flip op: %s" other)))) + +(defun day8/try-flip (flip-at code position acc) + (day8/flip-at code flip-at) + (cl-loop for next = (day8/step code position acc) + when (equal 'loop (car next)) return nil + when (equal 'final (car next)) return (cdr next) + do (setq position (car next)) + do (setq acc (cdr next)))) + +(message "Solution to day8/2: %s" + (let ((flip-options (cl-loop for op being the elements of day8/input + using (index idx) + for opcode = (car op) + when (or (equal 'nop opcode) + (equal 'jmp opcode)) + collect idx))) + (cl-loop for flip-at in flip-options + for result = (day8/try-flip flip-at (copy-sequence day8/input) 0 0) + when result return result))) -- cgit 1.4.1