/// <summary>
/// performs a Branch and Bound search of the state space of partial tours
/// stops when time limit expires and uses BSSF as solution
/// </summary>
/// <returns>results array for GUI that contains three ints: cost of solution, time spent to find solution, number of solutions found during search (not counting initial BSSF estimate)</returns>
public string[] bBSolveProblem()
{
string[] results = new string[3];
int count = 0;
Stopwatch timer = new Stopwatch();
PriorityQueue queue = new PriorityQueue();
timer.Start();
greedySolveProblem();
queue.Insert(new PartialPath(CalculateInitialMatrix(), Cities));
/* While there are still partial paths on the queue,
* the best one is popped off and its children are generated.
* Those that are better than the bssf are added to the queue.
*/
while (timer.Elapsed.TotalMilliseconds < time_limit && !queue.Empty())
{
PartialPath currentNode = queue.DeleteMin();
if (currentNode.FullPath && currentNode.CompletePath)
{
TSPSolution potentialSolution = new TSPSolution(currentNode.Path);
if (potentialSolution.costOfRoute() < costOfBssf())
{
bssf = potentialSolution;
count++;
}
}
else if (currentNode.LowerBound < costOfBssf())
{
GenerateChildren(currentNode, queue);
}
}
timer.Stop();
results[COST] = costOfBssf().ToString();
results[TIME] = timer.Elapsed.ToString();
results[COUNT] = count.ToString();
Console.WriteLine("Branch & Bound Size: " + Cities.Length + " Random: " + Seed + " Path: " + costOfBssf().ToString() + " Time: " + timer.Elapsed.ToString());
return(results);
}
public int BBSolution(Stopwatch timer)
{
// Stats
int maxStates = 0;
int totalStates = 0;
int prunedStates = 0;
int count = 0;
PriorityQueue q = new PriorityQueue();
SubProblem initialSubProblem = new SubProblem(
this.CalculateCostMatrix(),
this.Cities.Length,
0,
new List <int>()
);
initialSubProblem.path.Add(0);
q.Add(initialSubProblem);
while (!q.Empty() && timer.ElapsedMilliseconds < this.time_limit)
{
// Update statistics
if (q.Size() > maxStates)
{
maxStates = q.Size();
}
++totalStates;
SubProblem subProblem = q.Pop();
if (subProblem.path.Count == this.Cities.Length &&
subProblem.path[subProblem.GetCurrentCityIndex()] != 0)
{
// The subproblem is a valid solution!
this.bssf = new TSPSolution(PathToRoute(subProblem.path));
count++;
}
else
{
if (subProblem.HasMorePaths())
{
for (int col = 0; col < this.Cities.Length; ++col)
{
if (subProblem.reducedMatrix[subProblem.GetCurrentCityIndex(), col] != double.PositiveInfinity)
{
if (subProblem.reducedMatrix[subProblem.GetCurrentCityIndex(), col] + subProblem.lowerBound < this.costOfBssf())
{
List <int> pathClone = new List <int>(subProblem.path);
SubProblem newProblem = new SubProblem(
(double[, ])subProblem.reducedMatrix.Clone(),
this.Cities.Length,
subProblem.lowerBound,
pathClone
);
newProblem.path.Add(col);
newProblem.BlockPaths(
subProblem.GetCurrentCityIndex(),
newProblem.GetCurrentCityIndex()
);
newProblem.ReduceCostMatrix();
q.Add(newProblem);
}
else
{
++prunedStates;
}
}
}
}
}
}
// Print stats
Console.WriteLine("Max # of states: {0}", maxStates);
Console.WriteLine("Total # number of states: {0}", totalStates);
Console.WriteLine("# of states pruned: {0}", prunedStates);
return(count);
}