/// <summary>
/// performs a Branch and Bound search of the state space of partial tours
/// stops when time limit expires and uses BSSF as solution
/// @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)
public string[] bBSolveProblem()
{
// counts the number of bssf updates / solutions found
int count = 0;
// counts the number of pruned states
int pruned = 0;
// counts the number of total states
int total_states = 0;
//container for results
string[] results = new string[3];
//priority queue implementation
HeapQueue myqueue = new HeapQueue();
Route = new ArrayList();
Stopwatch timer = new Stopwatch();
timer.Start();
Route.Clear();
//generate greedy bssf as initial guess
greedySolveProblem();
//initialize a matrix with all the cities
bBNode init = new bBNode(GetCities());
/**
* Starts at the first city (0).
* It doesn't matter where we start because we are looking for a "loop" of cities.
* And we don't want to repeatedly find the same solution by starting at a different city.
*/
bBNode root = new bBNode(init, 0);
bBNode next;
//initialize queue
myqueue.MakeQueue((int)Math.Pow(Cities.Length, 2), root);
total_states++;
//while the queue is not empty and we haven't hit the time limit . . .
while (!myqueue.IsEmpty() && timer.ElapsedMilliseconds < this.time_limit)
{
// take the top node in the queue
next = (bBNode)myqueue.DeleteBestRoute();
//if it has a better solution than the bssf, go deeper, otherwise, we prune it.
if (next.getBound() < bssf.costOfRoute())
{
// check if the route is finished
if (next.getRouteLength() == Cities.Length)
{
//We found a better solution!
bssf = new TSPSolution(next.getRoute());
count++;
}
else
{
// expand the node, and only insert the children that do better than the bssf
List <bBNode> children = next.Expand();
foreach (bBNode c in children)
{
total_states++;
if (c.getBound() < bssf.costOfRoute())
{
myqueue.Insert(c);
}
else
{
pruned++;
}
}
}
}
else
{
pruned++;
}
}
timer.Stop();
Console.WriteLine("**************************************");
Console.WriteLine("# cities: " + Cities.Length);
Console.WriteLine("# seed: " + _seed);
Console.WriteLine("RunningTime: " + timer.Elapsed);
Console.WriteLine("Best tour: " + costOfBssf());
Console.WriteLine("Max stored states: " + myqueue.getMaxStoredStates());
Console.WriteLine("Number of Solutions: " + count);
Console.WriteLine("Number total states: " + total_states);
Console.WriteLine("Total pruned states: " + pruned);
results[COST] = costOfBssf().ToString(); // load results array
results[TIME] = timer.Elapsed.ToString();
results[COUNT] = count.ToString();
return(results);
}
