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#lang br
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(require racket/file rackunit)
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(define (string->ints str) (map string->number (string-split str #px",\\s*")))
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(define (string->regs str) (list->vector (string->ints str)))
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(define ((binarize proc) x y) (if (proc x y) 1 0))
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(define (make-runner program [calling-thd (current-thread)])
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(thread (λ ()
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(define regs (string->regs program))
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(define (maybe-enlarge-regs ptr)
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(unless (< ptr (vector-length regs))
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(define newvec (make-vector (add1 ptr) 0))
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(vector-copy! newvec 0 regs)
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(set! regs newvec))
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regs)
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(define (reg-ref ptr) (vector-ref (maybe-enlarge-regs ptr) ptr))
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(define (reg-set! ptr val) (vector-set! (maybe-enlarge-regs ptr) ptr val))
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(define relative-base 0)
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(let/ec terminate
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(let loop ([ptr 0])
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(define inst (for/list ([c (in-string (~r (reg-ref ptr) #:min-width 5 #:pad-string "0"))])
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(string->number (string c))))
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(define-values (opcode resolve)
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(match inst
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[(list d4 d3 d2 d1 d0)
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(values (+ (* 10 d1) d0)
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(λ (ptr offset)
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(define parameter-value (match offset [1 d2] [2 d3] [3 d4]))
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(define ptr-resolver (match parameter-value
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[0 reg-ref] ; position
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[1 values] ; immediate
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[2 (compose1 (λ (ptr) (+ relative-base ptr)) reg-ref)])); relative
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(ptr-resolver (+ ptr offset))))]))
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(define next-ptr
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(match opcode
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[(or 1 2 7 8) ; 4-arity: add & multiply & compare
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(reg-set! (resolve ptr 3) ((match opcode
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[1 +]
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[2 *]
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[7 (binarize <)]
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[8 (binarize =)]) (reg-ref (resolve ptr 1)) (reg-ref (resolve ptr 2))))
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(+ ptr 4)]
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[(or 3 4 9) ; 2-arity: input & output
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(match opcode
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[3 (reg-set! (resolve ptr 1) (thread-receive))]
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[4 (thread-send calling-thd (reg-ref (resolve ptr 1)))]
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[9 (set! relative-base (+ relative-base (reg-ref (resolve ptr 1))))])
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(+ ptr 2)]
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[(or 5 6) ; 3-arity: jump
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(if ((match opcode
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[5 not]
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[6 values]) (zero? (reg-ref (resolve ptr 1))))
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(reg-ref (resolve ptr 2))
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(+ ptr 3))]
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[99 (thread-send calling-thd 'done) (terminate)]
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[_ (error "unknown opcode" opcode)]))
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(loop next-ptr))))))
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(define black 0)
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(define white 1)
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(define left +i)
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(define right -i)
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(define (paint-panels #:start initial-color)
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(define robot-program (make-runner (file->string "11.rktd")))
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(define panels (make-hasheqv))
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(let loop ([pos 0][dir +i])
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(when (thread-running? robot-program)
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(thread-send robot-program (hash-ref panels pos initial-color)))
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(match (thread-receive)
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['done panels]
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[new-color
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(hash-set! panels pos new-color)
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(define turn (match (thread-receive) [0 left] [1 right]))
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(define new-dir (* turn dir))
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(define new-pos (+ pos new-dir))
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(loop new-pos new-dir)])))
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;; 1
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(check-eq? (length (hash-keys (paint-panels #:start black))) 2478)
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;; 2
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(define white-panels (for/list ([(loc color) (in-hash (paint-panels #:start white))]
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#:when (eqv? color white))
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loc))
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(define rows (sort (group-by imag-part white-panels) > #:key (compose1 imag-part car)))
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(define (make-printable row)
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(define real-parts (map real-part row))
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(string-join (for/list ([i (in-range (add1 (apply max real-parts)))])
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(if (memq i real-parts) "X" " ")) ""))
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;; 2
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(define painted-rows (map make-printable rows))
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(check-equal? painted-rows
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'(" X X XX XXXX XXX X X XX XX XXXX" " X X X X X X X X X X X X X X" " XXXX X X X X X X X X X X" " X X X X XXX X X X XX XXXX X" " X X X X X X X X X X X X X X" " X X XX XXXX X X XX XXX X X XXXX"))
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(for-each displayln painted-rows)
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