/// <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 solutionCount = 0;
Stopwatch timer = new Stopwatch();
PriorityQueue <State> pQueue = new PriorityQueue <State>();
int maxStoredStates = 0;
int bssfUpdates = 0;
int totalStatesCreated = 0;
int totalStatesPruned = 0;
timer.Start();
string[] intialResults = defaultSolveProblem();
double bestCostSoFar = Int32.Parse(intialResults[COST]);
Console.WriteLine("BestCostSoFar: " + bestCostSoFar);
State initialState = initializeState();
this.reduceState(ref initialState);
pQueue.insert(initialState, (int)initialState.lowerBound);
while (!pQueue.isEmpty() && timer.Elapsed.Seconds < 60) // while queue is not empty or has not passed 60 seconds
{
State parentState = pQueue.deleteMin();
if (parentState.lowerBound >= bestCostSoFar) // trim queue if state has worse bound than bssf
{
totalStatesPruned++;
continue;
}
for (int i = 0; i < this.Cities.Length; i++)
{
if (!parentState.visited.Contains(i))
{
// createChild
totalStatesCreated++;
State childState = parentState.getCopy();
this.addCityToRoute(ref childState, i);
this.reduceState(ref childState);
if (childState.route.Count == this.Cities.Count()) // if route is complete
{
TSPSolution newSolution = new TSPSolution(childState.route);
double cost = newSolution.costOfRoute();
if (cost < bestCostSoFar)
{
bssfUpdates++;
bestCostSoFar = cost;
bssf.Route = childState.route;
}
}
else // route is not complete
{
if (childState.lowerBound < bestCostSoFar) // don't insert in queue if state has worse bound than bssf
{
pQueue.insert(childState, (int)childState.lowerBound);
if (pQueue.getCount() > maxStoredStates)
{
maxStoredStates = pQueue.getCount();
}
}
else
{
totalStatesPruned++;
}
}
}
}
}
timer.Stop();
results[COST] = costOfBssf().ToString();
results[TIME] = timer.Elapsed.ToString();
results[COUNT] = solutionCount.ToString();
Console.WriteLine("===================================");
Console.WriteLine("StatesCreated: " + totalStatesCreated);
Console.WriteLine("StatesPruned: " + totalStatesPruned);
Console.WriteLine("bssfUpdates: " + bssfUpdates);
Console.WriteLine("MaxStoredStates: " + maxStoredStates);
return(results);
}
