//returns number of updates to BSSF made during the exploration
private void explore(SearchSpace current, PriorityQ q)
{
List <int> citiesRemaining = current.CitiesRemaining;
bool leaf = true;
//O()
foreach (int city in citiesRemaining)
{
leaf = false;
SearchSpace child = new SearchSpace(current, city);//O(n^2)
statesCreated++;
if (child.Bound < costOfBssf())
{
q.Insert(child);
}
else
{
statesPruned++;
}
}
if (leaf)
{
TSPSolution possibleSoln = new TSPSolution(current.Route, Cities);
if (possibleSoln.costOfRoute() < costOfBssf())
{
bssf = possibleSoln;
solutionsFound++;
}
}
}
/// <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];
Stopwatch timer = new Stopwatch();
timer.Start();
double[,] graphMatrix = buildGraphMatrix();
defaultGetBSSF(); //replace with greedy or however you want to initialize BSSF
//build cityIndices list. Stupid but need it
List <int> cityIndices = initCityIndices(); //O(n)
//Build the q with the initial searchSpace having {0} as it's current route
PriorityQ q = new PriorityQ();
q.Makequeue(); //O(1)
q.Insert(new SearchSpace(new List <int>(), cityIndices, 0, graphMatrix, 0, _size)); //O(log|V|)
statesCreated++;
//Branch and bound.
//O(n^2n!)
while (q.NotEmpty() && timer.ElapsedMilliseconds < 60 * 1000) //could run O(n!) times
{
SearchSpace curr = q.Deletemin(); //O(log|V|)
if (curr.Bound < costOfBssf())
{
explore(curr, q);
}
else
{
statesPruned++;
}
}
timer.Stop();
results[COST] = costOfBssf().ToString(); // load results array
results[TIME] = timer.Elapsed.ToString();
results[COUNT] = solutionsFound.ToString();
statesStoredMax = q.MaxCount;
statesPruned += q.Count;
return(results);
}