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Knapsack problem/Bounded: Difference between revisions
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1 unit(s) socks 4 dag (value = 50)
</pre>
=={{header|Oz}}==
Using constraint programming.
<lang oz>declare
%% maps items to tuples of
%% Weight(hectogram), Value and available Pieces
Problem = knapsack('map':9#150#1
'compass':13#35#1
'water':153#200#2
'sandwich':50#60#2
'glucose':15#60#2
'tin':68#45#3
'banana':27#60#3
'apple':39#40#3
'cheese':23#30#1
'beer':52#10#3
'suntan cream':11#70#1
'camera':32#30#1
't-shirt':24#15#2
'trousers':48#10#2
'umbrella':73#40#1
'waterproof trousers':42#70#1
'waterproof overclothes':43#75#1
'note-case':22#80#1
'sunglasses':7#20#1
'towel':18#12#2
'socks':4#50#1
'book':30#10#2
)
%% item -> Weight
Weights = {Record.map Problem fun {$ X} X.1 end}
%% item -> Value
Values = {Record.map Problem fun {$ X} X.2 end}
proc {Knapsack Solution}
%% a solution maps items to finite domain variables
%% whose maximum values depend on the item type
Solution = {Record.map Problem fun {$ _#_#Max} {FD.int 0#Max} end}
%% no more than 400 hectograms
{FD.sumC Weights Solution '=<:' 400}
%% search through valid solutions
{FD.distribute naive Solution}
end
proc {PropagateLargerValue Old New}
%% propagate that new solutions must yield a higher value
%% than previously found solutions (essential for performance)
{FD.sumC Values New '>:' {Value Old}}
end
fun {Value Candidate}
{Record.foldL {Record.zip Candidate Values Number.'*'} Number.'+' 0}
end
fun {Weight Candidate}
{Record.foldL {Record.zip Candidate Weights Number.'*'} Number.'+' 0}
end
[Best] = {SearchBest Knapsack PropagateLargerValue}
in
{System.showInfo "Items: "}
{Record.forAllInd Best
proc {$ I V}
if V > 0 then
{System.showInfo I#": "#V}
end
end
}
{System.printInfo "\n"}
{System.showInfo "total value: "#{Value Best}}
{System.showInfo "total weight: "#{Weight Best}}</lang>
Output:
<pre>
Items:
banana: 3
cheese: 1
compass: 1
glucose: 2
map: 1
note-case: 1
socks: 1
sunglasses: 1
suntan cream: 1
water: 1
waterproof overclothes: 1
total value: 1010
total weight: 396
</pre>
Takes about 3 seconds on a slow netbook.
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