/// <summary>
/// Constructor for a candidate solution.
/// </summary>
/// <param name="items">List of all the items</param>
/// <param name="index">index (into the above list) of the last item to be added to this candidate solution</param>
/// <param name="previous">the remaining items</param>
public CandidateSolution(List <KnapsackItem> items, int index, CandidateSolution previous)
{
if (index == -1)
{
_index = index;
_value = 0;
_weight = 0;
_previous = null;
}
else
{
_index = index;
_value = previous.Value + items[index].Value;
_weight = previous.Weight + items[index].Weight;
_previous = previous;
}
}
/// <summary>
/// A method to compute the upper bound
/// </summary>
/// <param name="toCompute">The candidate solution whose upper bound we wish to compute</param>
/// <param name="foundSoFar">The best candidate solution we have found so far</param>
/// <returns>the upper bound</returns>
public int ComputeBounds(CandidateSolution toCompute, ref CandidateSolution best)
{
int i = toCompute.Index + 1;
while (i < _items.Count && (toCompute.Weight + _items[i].Weight) <= _weightLimit)
{
CandidateSolution newSolution = new CandidateSolution(_items, i, toCompute);
toCompute = newSolution;
i++;
}
if (toCompute.Value > best.Value)
{
best = toCompute;
}
if (i >= _items.Count || toCompute.Weight == _weightLimit)
{
return(toCompute.Value);
}
else
{
return((int)(((((long)(_weightLimit - toCompute.Weight) * (_items[i].Value)) - 1) / (_items[i].Weight)) + toCompute.Value));
}
}
/// <summary>
/// Method to find the optimal solution
/// </summary>
/// <param name="filename">input file</param>
public void Solve(string filename)
{
_weightLimit = ReadInput(filename);
CandidateSolution candidate = new CandidateSolution(_items, -1, null);
CandidateSolution best = candidate;
PriorityQueue <int, CandidateSolution> queue = new PriorityQueue <int, CandidateSolution>();
queue.Add(candidate, ComputeBounds(candidate, ref best));
while (queue.Count > 0 && queue.MaximumPriority >= best.Value)
{
CandidateSolution root = queue.RemoveMaximumPriority();
int k = root.Index + 1;
for (int j = k; j < _items.Count; j++)
{
CandidateSolution child = new CandidateSolution(_items, j, root);
if (child.Weight <= _weightLimit)
{
int childBounds = ComputeBounds(child, ref best);
if (childBounds > best.Value)
{
queue.Add(child, childBounds);
}
}
}
}
_totalValue = best.Value;
_totalWeight = best.Weight;
while (best.Previous != null)
{
KnapsackItem tmp = _items[best.Index];
tmp.SelectionText = "X";
_items[best.Index] = tmp;
best = best.Previous;
}
}
