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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 th (make-runner (file->string "15.rktd")))
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(define (step where)
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(thread-send th where)
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(match (thread-receive)
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[0 'wall]
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[1 'empty]
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[2 'oxygen]))
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(define (dir->cmd dir)
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(match dir
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[+i 1]
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[-i 2]
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[-1 3]
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[1 4]))
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(define (turn-left dir) (* dir +i))
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(define (turn-right dir) (/ dir +i))
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(require graph)
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(define g (unweighted-graph/undirected null))
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(define (explore loc [dir +i])
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(define left-dir (turn-left dir))
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(match (step (dir->cmd left-dir))
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['wall (explore loc (turn-right dir))]
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[eo (add-edge! g loc (+ loc left-dir))
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(match eo
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['empty (explore (+ loc left-dir) left-dir)]
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['oxygen (+ loc left-dir)])]))
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;; 1
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(define oxygen-loc (explore 0))
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(check-eq? (sub1 (length (fewest-vertices-path g 0 oxygen-loc))) 272)
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;; 2
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(define-values (path-lengths _) (bellman-ford g oxygen-loc))
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(check-eq? (apply max (hash-values path-lengths)) 398)
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