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  1. ; water jugs puzzle
  2.  
  3. (define (water-jugs-verbose fcap tcap target)
  4.   (let loop ((fjug 0) (tjug 0) (steps 0))
  5.     (display "step: ") (display steps)
  6.     (display "; fjug: ") (display fjug)
  7.     (display "; tjug: ") (display tjug)
  8.     (cond ((= fjug target)
  9.             (display "; done; target in fjug") (newline)
  10.             steps)
  11.           ((= tjug target)
  12.             (display "; done; target in tjug") (newline)
  13.             steps)
  14.           ((= tjug tcap) ; "to" jug full; empty it
  15.             (display "; tjug full; empty it") (newline)
  16.             (loop fjug 0 (+ steps 1)))
  17.           ((zero? fjug)
  18.             (display "; fjug empty; fill it") (newline)
  19.             (loop fcap tjug (+ steps 1)))
  20.           (else
  21.             (display "; pour fjug into tjug") (newline)
  22.             (let ((x (min (- tcap tjug) fjug)))
  23.               (loop (- fjug x) (+ tjug x) (+ steps 1)))))))
  24.  
  25. (define (water-jugs fcap tcap target)
  26.   (let loop ((fjug 0) (tjug 0) (steps 0))
  27.     (cond ((or (= fjug target) (= tjug target)) steps)
  28.           ((= tjug tcap) (loop fjug 0 (+ steps 1)))
  29.           ((zero? fjug) (loop fcap tjug (+ steps 1)))
  30.           (else (let ((x (min (- tcap tjug) fjug)))
  31.             (loop (- fjug x) (+ tjug x) (+ steps 1)))))))
  32.  
  33. (define (jugs x y target)
  34.   (if (positive? (modulo target (gcd x y))) #f
  35.     (min (water-jugs x y target) (water-jugs y x target))))
  36.  
  37. (water-jugs-verbose 3 5 4) (newline)
  38. (water-jugs-verbose 5 3 4) (newline)
  39. (display (jugs 3 5 4)) (newline)
Success #stdin #stdout 0.02s 8800KB
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stdin
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Standard input is empty
stdout
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step: 0; fjug: 0; tjug: 0; fjug empty; fill it
step: 1; fjug: 3; tjug: 0; pour fjug into tjug
step: 2; fjug: 0; tjug: 3; fjug empty; fill it
step: 3; fjug: 3; tjug: 3; pour fjug into tjug
step: 4; fjug: 1; tjug: 5; tjug full; empty it
step: 5; fjug: 1; tjug: 0; pour fjug into tjug
step: 6; fjug: 0; tjug: 1; fjug empty; fill it
step: 7; fjug: 3; tjug: 1; pour fjug into tjug
step: 8; fjug: 0; tjug: 4; done; target in tjug

step: 0; fjug: 0; tjug: 0; fjug empty; fill it
step: 1; fjug: 5; tjug: 0; pour fjug into tjug
step: 2; fjug: 2; tjug: 3; tjug full; empty it
step: 3; fjug: 2; tjug: 0; pour fjug into tjug
step: 4; fjug: 0; tjug: 2; fjug empty; fill it
step: 5; fjug: 5; tjug: 2; pour fjug into tjug
step: 6; fjug: 4; tjug: 3; done; target in fjug

6
https://ideone.com/dy2IzB
language:
Scheme (guile 2.2.4)
created:
7 years ago
visibility:
public

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