protected BackPackingSolverBase(List <BackPackItem> items, double capacity)
{
_theVault = new ItemVault();
_theBackPack = new BackPack(capacity);
foreach (var item in items)
{
_theVault.AddItem(item);
}
}
/// <summary>
/// The solver follows these steps:
/// 1) Select the "best" item from the Vault (see PickBestItemFromVault).
/// If (a description of) an item is returned, then
/// 2) Remove the item from the Vault.
/// 3) Add the item to the Backpack.
/// 4) Call Solve again (the weight capacity will now be reduced).
/// </summary>
public override void Solve(ItemVault theItemVault, BackPack theBackPack)
{
string description = PickNextItemFromVault(theItemVault, theBackPack.WeightCapacityLeft);
if (description != string.Empty)
{
BackPackItem item = theItemVault.RemoveItem(description);
theBackPack.AddItem(item);
Solve(theItemVault, theBackPack);
}
}
/// <summary>
/// This method picks the "best" item currently in the Vault.
/// "Best" is defined as the item for which it holds that:
/// 1) The weight of the item does not exceed the given limit.
/// 2) No other item (for which 1) holds) has a higher
/// "actual item value". The calculation of "actual item value"
/// is deferred to derived classes.
/// </summary>
/// <returns>
/// Identifier for the "best" item (String.Empty if no item found)
/// </returns>
private string PickNextItemFromVault(ItemVault theItemVault, double weightLimit)
{
double bestValue = 0;
BackPackItem bestItem = null;
foreach (var item in theItemVault.Items)
{
if (item.Weight <= weightLimit)
{
double candidateValue = ActualItemValue(item);
if (candidateValue > bestValue)
{
bestValue = candidateValue;
bestItem = item;
}
}
}
return((bestItem != null) ? bestItem.Description : string.Empty);
}
/// <summary>
/// This method just returns the first item in the Vault, if
/// 1) Any items are left at all, and
/// 2) The weight of the item does not exceed the given limit.
/// Yes, this is a pretty stupid approach...
/// </summary>
/// <returns>
/// Identifier for the next item (String.Empty if no item found)
/// </returns>
private string PickNextItemFromVault(ItemVault theItemVault, double weightLimit)
{
return((theItemVault.Items.Count > 0 && theItemVault.Items[0].Weight <= weightLimit)
? theItemVault.Items[0].Description
: String.Empty);
}
/// <summary> /// Override this method to implement a specific algorithm /// for backpacking. /// </summary> public abstract void Solve(ItemVault theItemVault, BackPack theBackPack);
