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Matthew Butterick 5 years ago
parent 34310ca3fc
commit b98bf1265a
2 changed files with 95 additions and 0 deletions
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2019/19.rkt
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#lang br
(require racket/file rackunit racket/set)
(define (string->ints str) (map string->number (string-split str #px",\\s*")))
(define (string->regs str) (list->vector (string->ints str)))
(define ((binarize proc) x y) (if (proc x y) 1 0))
(define (make-runner program [calling-thd (current-thread)])
(thread (λ ()
(define regs (string->regs program))
(define (maybe-enlarge-regs ptr)
(unless (< ptr (vector-length regs))
(define newvec (make-vector (add1 ptr) 0))
(vector-copy! newvec 0 regs)
(set! regs newvec))
regs)
(define (reg-ref ptr) (vector-ref (maybe-enlarge-regs ptr) ptr))
(define (reg-set! ptr val) (vector-set! (maybe-enlarge-regs ptr) ptr val))
(define relative-base 0)
(let/ec terminate
(let loop ([ptr 0])
(define inst (for/list ([c (in-string (~r (reg-ref ptr) #:min-width 5 #:pad-string "0"))])
(string->number (string c))))
(define-values (opcode resolve)
(match inst
[(list d4 d3 d2 d1 d0)
(values (+ (* 10 d1) d0)
(λ (ptr offset)
(define parameter-value (match offset [1 d2] [2 d3] [3 d4]))
(define ptr-resolver (match parameter-value
[0 reg-ref] ; position
[1 values] ; immediate
[2 (compose1 (λ (ptr) (+ relative-base ptr)) reg-ref)])); relative
(ptr-resolver (+ ptr offset))))]))
(define next-ptr
(match opcode
[(or 1 2 7 8) ; 4-arity: add & multiply & compare
(reg-set! (resolve ptr 3) ((match opcode
[1 +]
[2 *]
[7 (binarize <)]
[8 (binarize =)]) (reg-ref (resolve ptr 1)) (reg-ref (resolve ptr 2))))
(+ ptr 4)]
[(or 3 4 9) ; 2-arity: input & output
(match opcode
[3 (reg-set! (resolve ptr 1) (thread-receive))]
[4 (thread-send calling-thd (reg-ref (resolve ptr 1)))]
[9 (set! relative-base (+ relative-base (reg-ref (resolve ptr 1))))])
(+ ptr 2)]
[(or 5 6) ; 3-arity: jump
(if ((match opcode
[5 not]
[6 values]) (zero? (reg-ref (resolve ptr 1))))
(reg-ref (resolve ptr 2))
(+ ptr 3))]
[99 (terminate)]
[_ (error "unknown opcode" opcode)]))
(loop next-ptr))))))
(define beam-rec (make-hasheq))
(define (in-beam? x y)
(hash-ref! beam-rec (+ (* 10000 x) y)
(λ ()
(define th (make-runner (file->string "19.rktd")))
(thread-send th x)
(thread-send th y)
(not (zero? (thread-receive))))))
;; 1
(check-eq?
(for*/sum ([x (in-range 50)]
[y (in-range 50)]
#:when (in-beam? x y))
1)
129)
(define (in-big-square? x y)
(and
(in-beam? x y)
(in-beam? (+ x 99) y)
(in-beam? x (+ y 99))))
;; 2
;; discovered by trial & error:
;; 2100 too low
;; 2200 ok
(check-eq?
(for*/first ([xy-sum (in-naturals 2100)]
[x (in-range xy-sum)]
[y (in-value (- xy-sum x))]
#:when (in-big-square? x y))
(+ (* 10000 x) y))
14040699)

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2019/19.rktd
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