38 lines
1.2 KiB
Racket
38 lines
1.2 KiB
Racket
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#lang racket
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(require racket/set
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"../lib.rkt")
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(define (parse instr)
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(match instr
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[(regexp #rx"(.+) (.+)" (list _ op arg))
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(cons (string->symbol op) (string->number arg))]))
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(define input (list->vector (map parse (problem-input 8))))
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(define (run instrs [part1 #f])
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(let loop ([pc 0] [acc 0] [ran (set)])
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(cond
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[(>= pc (vector-length instrs)) acc]
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[(set-member? ran pc) (if part1 acc #f)]
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[else (match (vector-ref instrs pc)
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[`(nop . ,arg) (loop (add1 pc) acc (set-add ran pc))]
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[`(acc . ,arg) (loop (add1 pc) (+ acc arg) (set-add ran pc))]
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[`(jmp . ,arg) (loop (+ pc arg) acc (set-add ran pc))])])))
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(define (try-run instrs)
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(for/last ([i (range (vector-length instrs))]
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#:when (member (car (vector-ref instrs i)) '(nop jmp)))
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(define acc
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(match-let* ([`(,op . ,arg) (vector-ref instrs i)]
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[op (if (symbol=? op 'nop) 'jmp 'nop)])
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(or (run instrs)
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(run (vector-set!* instrs i `(,op . ,arg))))))
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#:final acc
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acc))
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(define-values (part1 part2)
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(values (run input #t) (try-run input)))
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(show-solution part1 part2)
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