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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Knapsack-problem-Continuous/Racket/knapsack-problem-continuous.rkt Normal file
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#lang racket
(define shop-inventory
'((beef 3.8 36)
(pork 5.4 43)
(ham 3.6 90)
(greaves 2.4 45)
(flitch 4.0 30)
(brawn 2.5 56)
(welt 3.7 67)
(salami 3.0 95)
(sausage 5.9 98)))
(define (continuous-knapsack shop sack sack-capacity sack-total-value)
;; solved by loading up on the highest value item...
(define (value/kg item) (/ (third item) (second item)))
(if (zero? sack-capacity)
(values (reverse sack) sack-total-value)
(let* ((best-value-item (argmax value/kg shop))
(bvi-full-weight (second best-value-item))
(amount-can-take (min sack-capacity bvi-full-weight))
(bvi-full-value (third best-value-item))
(bvi-taken-value (* bvi-full-value (/ amount-can-take bvi-full-weight))))
(continuous-knapsack (remove best-value-item shop)
(cons (list (first best-value-item)
(if (= amount-can-take bvi-full-weight)
'all-of amount-can-take) bvi-taken-value)
sack)
(- sack-capacity amount-can-take)
(+ sack-total-value bvi-taken-value)))))
(define (report-knapsack sack total-value)
(for-each (lambda (item)
(if (eq? 'all-of (second item))
(printf "Take all of the ~a (for ~a)~%"
(first item) (third item))
(printf "Take ~a of the ~a (for ~a)~%"
(real->decimal-string (second item))
(first item)
(real->decimal-string (third item)))))
sack)
(printf "For a grand total of: ~a" (real->decimal-string total-value)))
(call-with-values (lambda () (continuous-knapsack shop-inventory null 15 0))
report-knapsack)