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Day 23: Keep track of whether elves have moved instead of doing set comparisons

This commit is contained in:
Jonathan Chan 2022-12-23 12:55:57 -08:00
parent 91f27e746f
commit a6e8936f7f
2 changed files with 9 additions and 6 deletions
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2
README.md
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@ -7,4 +7,4 @@ Approximate execution times of the hardest problems, compiled with `raco exe`.
| 15 | 3.81 | | 15 | 3.81 |
| 16 | 20.6 | | 16 | 20.6 |
| 19 | 75.7 | | 19 | 75.7 |
| 23 | 15.8 | | 23 | 14.0 |

13
src/23.rkt
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@ -67,14 +67,17 @@
(hash-update ps (apply (propose elves r) elf) #{cons elf %} '()))) (hash-update ps (apply (propose elves r) elf) #{cons elf %} '())))
(define (round elves r) (define (round elves r)
(for/fold ([elves* (set)]) (for/fold ([elves* (set)]
[moved? #f])
([(p es) (proposals elves r)]) ([(p es) (proposals elves r)])
(match es (match es
[`(,e1 ,e2) (set-add (set-add elves* e1) e2)] [`(,e1 ,e2) (values (set-add (set-add elves* e1) e2) moved?)]
[`(,e) (set-add elves* p)]))) [`(,e) #:when (not (equal? p e)) (values (set-add elves* p) #t)]
[`(,e) (values (set-add elves* p) moved?)])))
(define part1 (define part1
(for/fold ([elves elves] (for/fold ([elves elves]
[_ #f]
#:result (grounds elves)) #:result (grounds elves))
([r (in-range 10)]) ([r (in-range 10)])
(round elves r))) (round elves r)))
@ -82,7 +85,7 @@
(define part2 (define part2
(let loop ([elves elves] (let loop ([elves elves]
[r 1]) [r 1])
(define elves* (round elves r)) (define-values (elves* moved?) (round elves r))
(if (set=? elves elves*) (add1 r) (loop elves* (add1 r))))) (if moved? (loop elves* (add1 r)) (add1 r))))
(show-solution part1 part2) (show-solution part1 part2)