Sync

Task/Knapsack-problem-Unbounded/Racket/knapsack-problem-unbounded.rkt

@@ -0,0 +1,39 @@
+#lang racket
+
+(struct item (name explanation value weight volume) #:prefab)
+
+(define items
+  (list
+   (item "panacea (vials of)" "Incredible healing properties" 3000 0.3 0.025)
+   (item "ichor (ampules of)" "Vampires blood"                1800 0.2 0.015)
+   (item "gold (bars)"        "Shiney shiney"                 2500 2.0 0.002)))
+
+(define (fill-sack items volume-left weight-left sack sack-value)
+  (match items
+    ['() (values (list sack) sack-value)]
+    [(cons (and (item _ _ item-val weight volume) item) items)
+     (define max-q-wgt (floor (/ weight-left weight)))
+     (define max-q-vol (floor (/ volume-left volume)))
+     (for/fold ([best (list sack)] [best-val sack-value])
+               ([n (exact-round (add1 (min max-q-vol max-q-wgt)))])
+       (define-values [best* best-val*]
+         (fill-sack items
+                    (- volume-left (* n volume))
+                    (- weight-left (* n weight))
+                    (cons (cons n item) sack)
+                    (+ sack-value (* n item-val))))
+       (cond [(> best-val* best-val) (values best* best-val*)]
+             [(= best-val* best-val) (values (append best best*) best-val*)]
+             [else                   (values best best-val)]))]))
+
+(define (display-sack sack total)
+  (for ([sk sack])
+    (define qty (car sk))
+    (define name (item-name (cdr sk)))
+    (if (zero? qty)
+      (printf "Leave ~a\n" name)
+      (printf "Take ~a ~a\n" qty name)))
+  (printf "GRAND TOTAL: ~a\n\n" total))
+
+(call-with-values (λ() (fill-sack items 0.25 25 '() 0))
+                  (λ(sacks total) (for ([s sacks]) (display-sack s total))))