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aoc-racket/2020/22.rkt

40 lines
1.5 KiB
Racket

#lang br
(require racket/file rackunit racket/set)
(struct result (who cards) #:transparent)
(match-define (list p1s p2s)
(let* ([str (file->string "22.rktd")]
[strs (string-split str "\n\n")])
(map (λ (str) (cdr (map string->number (string-split str "\n")))) strs)))
(define (play-game p1s p2s [recursive #false])
(define game-states (mutable-set))
(let/ec exit
(for/fold ([p1s p1s] [p2s p2s]
#:result (if (empty? p1s) (result 'p2 p2s) (result 'p1 p1s)))
([i (in-naturals)]
#:break (or (empty? p1s) (empty? p2s)))
(match-define (list (cons p1 p1s-rest) (cons p2 p2s-rest)) (list p1s p2s))
(define (p1-wins) (values (append p1s-rest (list p1 p2)) p2s-rest))
(define (p2-wins) (values p1s-rest (append p2s-rest (list p2 p1))))
(cond
[(and recursive
(let ([game-state (cons p1s p2s)])
(when (set-member? game-states game-state)
(exit (result 'p1 p1s)))
(set-add! game-states game-state))
(<= p1 (length p1s-rest)) (<= p2 (length p2s-rest)))
(match (play-game (take p1s-rest p1) (take p2s-rest p2) #true)
[(result 'p1 _) (p1-wins)]
[_ (p2-wins)])]
[(> p1 p2) (p1-wins)]
[else (p2-wins)]))))
(define (winner->score winner)
(for/sum ([(val i) (in-indexed (reverse (result-cards winner)))])
(* val (add1 i))))
(check-equal? (winner->score (play-game p1s p2s)) 30138)
(check-equal? (winner->score (play-game p1s p2s #true)) 31587)