public override DecisionResult Solve(DecisionKnapsackInstance instance)
{
//the list is being processed backwards in the algorithm, so it must be sorted in ascending order
instance.Items = instance.Items.OrderBy(a => a.Weight).ToList();
return(new DecisionBranchBound().Solve(instance));
}
bool DoesSolutionExist(int itemsRemaining, int currentPrice,
int currentWeight, int maxRemainingPrice, DecisionKnapsackInstance knapsackInstance)
{
numberOfSteps++;
if (currentWeight > knapsackInstance.KnapsackSize)
{
return(false);
}
if (maxRemainingPrice < knapsackInstance.MinimalPrice)
{
return(false);
}
if (itemsRemaining == 0)
{
return(currentWeight <= knapsackInstance.KnapsackSize && currentPrice >= knapsackInstance.MinimalPrice);
}
KnapsackItem currentItem = knapsackInstance.Items[itemsRemaining - 1];
//Put item in
if (DoesSolutionExist(itemsRemaining - 1, currentPrice + currentItem.Price, currentWeight + currentItem.Weight, maxRemainingPrice, knapsackInstance))
{
return(true);
}
//Don't put item in
if (DoesSolutionExist(itemsRemaining - 1, currentPrice, currentWeight, maxRemainingPrice - currentItem.Price, knapsackInstance))
{
return(true);
}
return(false);
}
public override DecisionSolution Solve(DecisionKnapsackInstance instance)
{
var priceSum = instance.GetPriceOfAllItems();
if (instance.MinimalPrice > priceSum)
{
return new DecisionSolution {
KnapsackInstance = instance, NumberOfSteps = 1, PermutationExists = false
}
}
;
if (instance.MinimalPrice == 0)
{
return new DecisionSolution {
KnapsackInstance = instance, NumberOfSteps = 1, PermutationExists = true
}
}
;
var priceRange = Math.Max(0.01, priceSum - instance.MinimalPrice);
//the list is being processed backwards in the algorithm, so it must be sorted in ascending order
instance.Items = instance.Items.OrderBy(a => Math.Max(a.Weight / instance.KnapsackSize, a.Price / priceRange)).
ToList();
return(new DecisionBranchBound().Solve(instance));
}
}
}
public override DecisionSolution Solve(DecisionKnapsackInstance knapsackInstance)
{
numberOfSteps = 0;
bool permutationExists = DoesSolutionExist(knapsackInstance.Items.Count, 0, 0, knapsackInstance);
return(new DecisionSolution {
KnapsackInstance = knapsackInstance, NumberOfSteps = numberOfSteps, PermutationExists = permutationExists
});
}
public abstract DecisionSolution Solve(DecisionKnapsackInstance instance);