// Initial state, reduces matrix
public State(City[] cities)
{
queue = new HeapPriorityQueue<State>(10000);
root = this;
Watch = new Stopwatch();
Watch.Start();
State.cities = cities;
cityCount = cities.Length;
matrix = new double[cities.Length, cities.Length];
for (int i = 0; i < cities.Length; i++)
{
for (int j = 0; j < cities.Length; j++)
{
matrix[i, j] = cities[i].costToGetTo(cities[j]);
// Set diagonals to infinity (negative)
if (i == j)
{
matrix[i, j] = double.PositiveInfinity;
}
}
}
bound = 0;
route = new ArrayList();
visited = new ArrayList();
pathsLeft = cityCount;
setInitialBSSF();
reduceMatrix();
// Start expanding until agenda is empty, time is up, or BSSF cost is equal to original LB.
Expand();
}
public State(State state)
{
Matrix = new Matrix(state.Matrix);
LowerBound = state.LowerBound;
_cityFrom = (int[])state._cityFrom.Clone();
_cityTo = (int[])state._cityTo.Clone();
_citiesInSolution = state._citiesInSolution;
}
public LbDifferenceResult(State includeState, State excludeState, double lowerBoundDifference, int fromCity, int toCity)
{
IncludeState = includeState;
ExcludeState = excludeState;
LowerBoundDifference = lowerBoundDifference;
FromCity = fromCity;
ToCity = toCity;
}
public void Add(State newState)
{
int position = newState.routeSF.Count;
System.Console.WriteLine(position);
if (_states[position] == null)
_states[position] = new ArrayList();
_states[position].Add(newState);
count++;
if (count > _maxCount)
_maxCount = count;
}
//O(n^2)
public State makeExclude(int x, int y, State state)
{
State excludeState = new State(copyMatrix(state.getMap()), state.getLB(), state.getEdges()); //O(n^2)
excludeState.setPoint(x, y, double.PositiveInfinity); //make chosen point infinity
reduceMatrix(excludeState); //O(n^2)
excludeState.setEdges(state.getEdges()); //initialize excludeStates edges
return excludeState;
}
//O(n)
public bool isDictionaryFilled(State state)
{
//returns whether or not the all of the edges have been added
for (int i = 0; i < state.getEdges().Count; i++)
{
if (state.getEdge(i) == -1)
return false; //if one hasn't been added, then it isn't full
}
return true;
}
//O(n^3)
public void findGreatestDiff(State state)
{
int chosenX = 0; //city x to city y
int chosenY = 0;
double greatestDiff = double.NegativeInfinity; //initialize to -oo to find what the greatest
//difference is
List<PointF> points = new List<PointF>();
for (int i = 0; i < state.getMap().GetLength(0); i++) //rows, O(n)
{
for (int j = 0; j < state.getMap().GetLength(1); j++) //columns
{
if (state.getPoint(i, j) == 0) //if point is 0
{
points.Add(new PointF(i, j)); //store all 0's in a point array
}
}
}
for (int i = 0; i < points.Count; i++) //loop through 0's to find the greatest difference
{//O(n^3) there will be atmost n points, because the entire
//matrix will be 0
int possibleMax = findExcludeMinusInclude(Convert.ToInt32(points[i].X), Convert.ToInt32(points[i].Y), state); //O(n^2)
if (possibleMax >= greatestDiff) //set the point to point values, if it is 0 is covered by =
{
chosenX = Convert.ToInt32(points[i].X);
chosenY = Convert.ToInt32(points[i].Y);
greatestDiff = possibleMax;
}
}
State include = makeInclude(chosenX, chosenY, state); //O(n^2)
if (BSSF > include.getLB()) //if include's lowerbound is better than the BSSF
{
include.setEdge(chosenX, chosenY); //set the edge in the dictionary
checkCycles(include, chosenX, chosenY); //O(n), make sure there are no potential cycles
queue.Add(include); //add to the queue to be popped off later
}
if (isDictionaryFilled(include))//O(n), have all of the edges been filled? then the include.LB is better
{ //than the current BSSF, set the BSSF
BSSF = include.getLB();
bestState = include; //save the "bestState"
}
State exclude = makeExclude(chosenX, chosenY, state);//O(n^2)
if (BSSF > exclude.getLB()) //if exclude's lowerbound is than the BSSF, add it to the queue
queue.Add(exclude);
if (isDictionaryFilled(exclude))//O(n), have all of the edges been filled?
{ // then exclude's lowerbound is better, set the BSSF to exclude.LB
BSSF = exclude.getLB();
bestState = exclude;
}
}
//O(n^2)
public int findExcludeMinusInclude(int x, int y, State state)
{
//finds the exlude minus the include of a point in a matrix
State excludeState = makeExclude(x, y, state); //O(n^2)
reduceMatrix(excludeState);//O(n^2)
State includeState = makeInclude(x, y, state); //O(n^2)
reduceMatrix(includeState); //O(n^2)
int cost = Convert.ToInt32(excludeState.getLB() - includeState.getLB());
return cost;
}
//O(n)
public void checkCycles(State state, int i, int j)
{
Dictionary<int, int> edges = new Dictionary<int, int>(state.getEdges());
if (getDictionarySize(edges) == edges.Count) //if the dictionary is full, stop
return;
int[] entered = new int[edges.Count];
int[] exited = new int[edges.Count];
for (int x = 0; x < entered.Length; x++) //O(n)
entered[x] = -1;
for (int x = 0; x < edges.Count; x++) //O(n)
{
exited[x] = edges[x];
if (exited[x] != -1)
entered[exited[x]] = x;
}
//the two loops above "flip" the arrays with value and index, e.g. if
//entered contained [0]=2, [1]=0, [2]=1
//exited will now contain [0]=1, [1]=2, [2]=0
entered[j] = i;
exited[i] = j;
int start = i;
int end = j;
while (exited[end] != -1) //O(n)
end = exited[end];
while (entered[start] != -1)//O(n)
start = entered[start];
if (getDictionarySize(edges) != edges.Count - 1) //if there is only one point left to fill,
{ //this will think there is a cycle, so make
while (start != j) //O(n) make sure there isn't one element left
{
state.setPoint(end, start, double.PositiveInfinity);
state.setPoint(j, start, double.PositiveInfinity);
start = exited[start];
}
}
}
public void branchAndBoundSolve()
{
initialState = new State(new Double[Cities.Length, Cities.Length]);
timer = new Stopwatch();
timer.Start();
for (int i = 0; i < Cities.Length; i++) //O(n^2), initialize initialStates map
{
for (int x = 0; x < Cities.Length; x++)
{
initialState.setPoint(i, x, Cities[i].costToGetTo(Cities[x]));
if (initialState.getPoint(i, x) == 0)
initialState.setPoint(i, x, double.PositiveInfinity);
}
}
initialState.initializeEdges(); //initializeEdges initializes the state's dictionary
//with key 0 to n (# of cities), value -> -1
reduceMatrix(initialState); //reduce the matrix to find lower bound
queue = new IntervalHeap<State>(); //this is a global queue
BSSF = greedy(); //find initial best solution so far, O(n^4)
Console.WriteLine("BSSF: " + BSSF);
findGreatestDiff(initialState); //exclude minus include, O(n^3)
TimeSpan ts = timer.Elapsed;
bool terminatedEarly = false; //boolean to keep track if we stopped after 30 seconds
int maxStates = 0; //keeps track of the maximum amount of states in the queue at one point
int totalSeconds = 0;
while (queue.Count != 0) //O(2^n * n^3), because each time you expand a node, it expands it 2 times, exponentially
{ //where n is the number of cities
if (queue.Count > maxStates) //if maxStates needs to be updated, update it
maxStates = queue.Count;
ts = timer.Elapsed;
State min = queue.DeleteMin();
if (totalSeconds < ts.Seconds)
{
totalSeconds = ts.Seconds;
Console.WriteLine("seconds: " + totalSeconds);
}
if (min.getLB() < BSSF) //if the min popped off the queue has a lowerbound less than
findGreatestDiff(min);//the BSSF, expand it, otherwise, prune it. -> O(n^3)
else
{//all of the lowerbounds are worse than the BSSF, break!
break;
}
}
if (!terminatedEarly)//if it solved the problem in less than 30 seconds
{
int city = 0;
for (int i = 0; i < bestState.getEdges().Count; i++) //O(n)
{
if (i == 0) //outputting a map into the Route list
{
Route.Add(Cities[i]);
city = bestState.getEdge(i);
}
else
{
Route.Add(Cities[city]);
city = bestState.getEdge(city);
}
}
bssf = new TSPSolution(Route);
// update the cost of the tour.
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
Program.MainForm.tbElapsedTime.Text = ts.TotalSeconds.ToString();
// do a refresh.
Program.MainForm.Invalidate();
}
}
public IncludeExcludeStates(State includeState, State excludeState)
{
this.includeState = includeState;
this.excludeState = excludeState;
}
/**
* This method updates the nodes in the queue after inserting a new node
* Time Complexity: O(log(|V|)) as reording the heap works by bubbling up the min value to the top
* which takes as long as the depth of the tree which is log|V|.
* Space Complexity: O(1) as it does not create any extra variables that vary with the size of the input.
*/
public void insert(State newState)
{
// update the count
count++;
states[count] = newState;
if (count > maxNum)
maxNum = count;
// as long as its parent has a larger value and have not hit the root
int indexIterator = count;
while (indexIterator > 1 && states[indexIterator / 2].getPriority() > states[indexIterator].getPriority())
{
// swap the two nodes
State temp = states[indexIterator / 2];
states[indexIterator / 2] = states[indexIterator];
states[indexIterator] = temp;
indexIterator /= 2;
}
}
/// <summary>
/// solve the problem. This is the entry point for the solver when the run button is clicked
/// right now it just picks a simple solution.
/// </summary>
public void solveProblem()
{
int x;
Route = new ArrayList();
ArrayList CitiesLeft = new ArrayList();
for (x = 0; x < Cities.Length; x++)
{
CitiesLeft.Add( Cities[Cities.Length - x - 1]);
}
City curCity = (City)CitiesLeft[0];
Route.Add(curCity);
CitiesLeft.RemoveAt(0);
while (CitiesLeft.Count > 0)
{
double minDist = 999999;
int minInd = 0;
for (int i = 0; i < CitiesLeft.Count; i++)
{
City temp = (City)CitiesLeft[i];
if (curCity.costToGetTo(temp) < minDist)
{
minDist = curCity.costToGetTo(temp);
minInd = i;
}
}
Program.MainForm.tbCostOfTour.Text += "Ind " + minInd;
curCity = (City)CitiesLeft[minInd];
Route.Add(curCity);
CitiesLeft.RemoveAt(minInd);
}
// call this the best solution so far. bssf is the route that will be drawn by the Draw method.
bssf = new TSPSolution(Route);
// update the cost of the tour.
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
Program.MainForm.tbElapsedTime.Text = "initial bssf";
// do a refresh.
Program.MainForm.Invalidate();
//My solving begins here
//generate first adjacency matrix
double[,] firstAdj = new double[Cities.Length,Cities.Length];
for (int i = 0; i < Cities.Length; i++)
{
for (int j = 0; j < Cities.Length; j++)
{
if (i == j)
firstAdj[i, j] = 999999;
else
firstAdj[i, j] = Cities[i].costToGetTo(Cities[j]);
}
}
State firstState = new State(firstAdj);
Agenda myAgenda = new Agenda(Cities.Length);
myAgenda.Add(firstState);
//Start timer and go
DateTime start = DateTime.Now;
DateTime timeUp = DateTime.Now.AddSeconds(60);
while ((myAgenda.hasNextState()) && (DateTime.Now <= timeUp))
{
State s = myAgenda.nextState;
if ((s.routeSF.Count == Cities.Length) && s.costSF < bssf.costOfRoute())
{
TSPSolution posS = new TSPSolution(s.routeSF);
if (posS.costOfRoute() < bssf.costOfRoute())
{
bssf = posS;
//Prune the agenda
myAgenda.Prune(bssf.costOfRoute());
// update the cost of the tour.
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
Program.MainForm.tbElapsedTime.Text = " " + (DateTime.Now - start);
// do a refresh.
Program.MainForm.Invalidate();
}
}
else
{
ArrayList newStates = s.Expand(Cities);
foreach (State state in newStates)
{
if (state.lowerBound < bssf.costOfRoute())
myAgenda.Add(state);
}
}
}
if (DateTime.Now < timeUp)
Program.MainForm.tbElapsedTime.Text += " true";
Program.MainForm.tbCostOfTour.Text += " MC " + myAgenda.MaxCount + " NP " + myAgenda.NumPruned;
}
//O(n^2)
public State makeInclude(int x, int y, State state)
{
State includeState = new State(copyMatrix(state.getMap()), state.getLB(), state.getEdges()); //O(n^2)
includeState.setPoint(y, x, double.PositiveInfinity); //set the "opposite point to infinity"
for (int j = 0; j < includeState.getMap().GetLength(1); j++) //set the row to infinity, O(n)
{
includeState.setPoint(x, j, double.PositiveInfinity);
}
for (int i = 0; i < includeState.getMap().GetLength(0); i++) //set the column to infinity, O(n)
{
includeState.setPoint(i, y, double.PositiveInfinity);
}
reduceMatrix(includeState); //O(n^2)
includeState.setEdges(state.getEdges()); //initialize includeState's dictionary of edges
return includeState;
}
// Copy constructor for making children (Josh)
// Reduces matrix based on whether edge is included
// Adds state to queue
public State(State parent, Boolean include, int from, int to)
{
matrix = (double[,])parent.matrix.Clone();
route = new ArrayList(parent.route);
visited = new ArrayList(parent.visited);
bound = parent.bound;
this.parent = parent;
depth = parent.depth + 1;
if (include)
{
bound += matrix[from, to];
pathsLeft = parent.pathsLeft - 1;
visited.Add(from);
visited.Add(to);
for (int i = 0; i < cityCount; i++)
{
matrix[from, i] = double.PositiveInfinity;
matrix[i, to] = double.PositiveInfinity;
}
// If there's more than one path left, delete paths to used vertices (Josh)
if (pathsLeft > 2)
{
for (int i = 0; i < visited.Count; i++)
{
matrix[to, (int)visited[i]] = double.PositiveInfinity;
// Shouldn't be necessary, but who knows?
matrix[(int)visited[i], from] = double.PositiveInfinity;
}
}
else if (pathsLeft == 2)
{
//this should keep the path from the final city back to the first one
for (int i = 1; i < visited.Count; i++)
{
matrix[to, (int)visited[i]] = double.PositiveInfinity;
// Shouldn't be necessary, but who knows?
matrix[(int)visited[i], from] = double.PositiveInfinity;
}
}
matrix[to, from] = double.PositiveInfinity;
}
else
{
matrix[from, to] = double.PositiveInfinity;
pathsLeft = parent.pathsLeft;
}
reduceMatrix();
// set BSSF if necessary (Josh)
// If not, set BSSF if necessary (Josh)
if (pathsLeft == 1)
{
for (int i = 0; i < cityCount; i++)
{
for (int j = 0; j < cityCount; j++)
{
if (matrix[i, j] != double.PositiveInfinity)
{
includeChild = new State(this, true, i, j);
Console.WriteLine("Found solution");
for (int k = 0; k < includeChild.visited.Count; k++)
{
Console.WriteLine(includeChild.visited[k]);
}
if (includeChild.bound < BSSF.bound)
{
// Calculate route from visited nodes
includeChild.calculateRoute();
BSSF = includeChild;
// Prune states starting with root
root.prune();
}
else
{
return;
}
}
}
}
}
// Add to queue
if (pathsLeft > 0 && bound < BSSF.bound)
{
queue.Enqueue(this, Priority);
}
}
private ArrayList generateChildren(State u)
{
ArrayList children = new ArrayList();
int row = (int)u.path[(u.path.Count-1)];
for (int i = 0; i < Cities.Length; i++)
{
if (u.matrix[row, i] != double.MaxValue && !u.path.Contains(i))
{
State child = new State(u);
child.path.Add(i);
child.boundValue += child.matrix[row, i];
for (int j = 0; j < Cities.Length; j++)
{
child.matrix[row, j] = double.MaxValue;
child.matrix[j, i] = double.MaxValue;
}
child.calculateBound();
children.Add(child);
}
}
return children;
}
// Finds initial BSSF (Brian)
// Call after setting cost matrix
// Use vertices to the right (or left) of the diagonal
// Cost matrix of initial BSSF, doesn't matter
// Only the route and bound matter
// So don't worry about the rest of the fields
public void setInitialBSSF()
{
ArrayList bssfCities = new ArrayList();
double cost = 0;
// TODO: fill this in
for (int i = 0; i < cityCount; i++)
{
bssfCities.Add(cities[(i + 1) % cityCount]);
cost += matrix[(i + 1) % cityCount, i];
}
BSSF = new State(bssfCities, cost);
}
public State(State m)
{
this.path = (ArrayList) m.path.Clone();
this.matrix = (double[,]) m.matrix.Clone();
this.boundValue = m.boundValue;
}
private State initState()
{
State s = new State();
s.matrix = new double[Cities.Length, Cities.Length];
for (int i = 0; i < Cities.Length; i++)
{
for (int j = 0; j < Cities.Length; j++)
{
double entry = Cities[i].costToGetTo(Cities[j]);
if (entry == 0)
entry = double.MaxValue;
s.matrix[i, j] = entry;
}
}
s.calculateBound();
return s;
}
//O(n^2)
public void reduceMatrix(State currentState)
{
double lowerBound = currentState.getLB();
for (int i = 0; i < currentState.getMap().GetLength(0); i++) // reduce rows
{//O(n^2)
double minimum = double.PositiveInfinity; //find the lowest value in that row to reduce
for (int j = 0; j < currentState.getMap().GetLength(1); j++)
{
if (currentState.getPoint(i, j) < minimum)
minimum = currentState.getPoint(i, j);
}
if (minimum == 0) //if there is already a 0 in that row, don't waste time looping through it
continue;
if (minimum != double.PositiveInfinity)
{
for (int j = 0; j < currentState.getMap().GetLength(1); j++)
{ //reduce the other entire row by that value
double reducedPoint = currentState.getPoint(i, j) - minimum;
currentState.setPoint(i, j, reducedPoint);
}
lowerBound += minimum; //add that lowest value to the lowerBound
}
}
for (int j = 0; j < currentState.getMap().GetLength(1); j++) //reduce columns
{//O(n^2)
double minimum = double.PositiveInfinity;
for (int i = 0; i < currentState.getMap().GetLength(0); i++)
{
if (currentState.getPoint(i, j) < minimum)
minimum = currentState.getPoint(i, j); //find the lowest value in the column
}
if (minimum == 0) //if there is already a 0 in that column, don't waste time looping through it
continue;
if (minimum != double.PositiveInfinity)
{
for (int i = 0; i < currentState.getMap().GetLength(0); i++)
{//reduce the entire column by that value
double lowerPoint = currentState.getPoint(i, j) - minimum;
currentState.setPoint(i, j, lowerPoint);
}
lowerBound += minimum; //add that minimum value to the lowerBound
}
}
currentState.setLB(lowerBound); //set the lowerbound
}
/// <summary>
/// solve the problem. This is the entry point for the solver when the run button is clicked
/// right now it just picks a simple solution.
/// </summary>
public void solveProblem()
{
State state = new State(Cities);
bssf = new TSPSolution(State.BSSF.Route);
Console.WriteLine(bssf.costOfRoute());
Console.WriteLine(State.BSSF.Bound);
Debug.Assert(bssf.costOfRoute() == State.BSSF.Bound);
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
Program.MainForm.tbElapsedTime.Text = State.Watch.Elapsed.ToString();
Program.MainForm.Invalidate();
// Trivial solution, what appeared here originally
// Uncomment to see how it works
/*int x;
Route = new ArrayList();
// this is the trivial solution.
for (x = 0; x < Cities.Length; x++)
{
Route.Add( Cities[Cities.Length - x -1]);
}
// call this the best solution so far. bssf is the route that will be drawn by the Draw method.
bssf = new TSPSolution(Route);
// update the cost of the tour.
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
// do a refresh.
Program.MainForm.Invalidate();*/
}
public ArrayList RunTSP(City[] Cities)
{
Route = new ArrayList();
Stopwatch timer = new Stopwatch();
bAndBTime = new TimeSpan();
timer.Start();
Greedy greedyAlgorithm = new Greedy(Cities);
ArrayList greedyRoute = greedyAlgorithm.RunGreedyTSP();
double[,] matrix = new double[Cities.Length, Cities.Length];
//Populate each array item with each respective edge cost
for (int i = 0; i < Cities.Length; i++)
{//O(n^2)
for (int j = 0; j < Cities.Length; j++)
{
if (i == j)
{
matrix[i, j] = double.PositiveInfinity;
}
else
{
matrix[i, j] = Cities[i].costToGetTo(Cities[j]);
}
}
}
IntervalHeap<State> queue = new IntervalHeap<State>();
double bestSolutionSoFar = greedyAlgorithm.BestSolutionSoFar();
bssfUpdatesAmt = 0;
prunedAmt = 0;
State bssfState = null;
totalStatesCreated = 0;
//Start with some problem
State curState = new State(matrix, 0, new Edge(-1, -1));
totalStatesCreated++;
//Reduce Matrix
//O(4n^2)
curState.Reduce();
//Let the queue be the set of active subproblems
//O(log(n))
queue.Add(curState);
maxQueueCount = 0;
bool timesUp = false;
while (queue.Count > 0)
{//O(2^n) or O(2^(8n^2 + 9n + 2log(n)))
if (timer.Elapsed.Seconds >= 30)
{
timesUp = true;
break;
}
//Choose a subproblem and remove it from the queue
if (queue.Count > maxQueueCount)
{
maxQueueCount = queue.Count;
}
//O(log(n))
curState = queue.DeleteMin();
if (curState.Cost() < bestSolutionSoFar)
{//O(8n^2 + 9n + 2log(n))
//For each lowest cost (each 0)
double highestScore = double.NegativeInfinity;
State[] includeExcludeStates = new State[2];
foreach (Edge edge in curState.LowestNums())
{//O(8n^2 + 9n)
//Include Matrix
State includeState = new State(curState, edge); //O(n)
totalStatesCreated++;
includeState.IncludeMatrix(edge.Row(), edge.Col()); //O(4n^2 + 7n)
//Exclude Matrix
State excludeState = new State(curState, edge); //O(n)
totalStatesCreated++;
excludeState.ExcludeMatrix(edge.Row(), edge.Col());//O(4n^2)
//Find the score for that edge (Exclude cost - Include cost)
double score = excludeState.Cost() - includeState.Cost();
if (score > highestScore)
{
includeExcludeStates[0] = includeState;
includeExcludeStates[1] = excludeState;
highestScore = score;
}
}
foreach (State subproblemState in includeExcludeStates)
{//O(2log(n))
//if each P (subproblem) chosen is a complete solution, update the bssf
if (subproblemState.CompleteSolution() && subproblemState.Cost() < bestSolutionSoFar)
{
bestSolutionSoFar = subproblemState.Cost();
bssfState = subproblemState;
bssfUpdatesAmt++;
}
//else if lowerBound < bestSolutionSoFar
else if (!subproblemState.CompleteSolution() && subproblemState.Cost() < bestSolutionSoFar)
{
//O(log(n))
queue.Add(subproblemState);
}
else
{
prunedAmt++;
}
}
}
}
if (!timesUp) prunedAmt += queue.Count;
//Call this the best solution so far. bssf is the route that will be drawn by the Draw method.
if (bssfState != null)
{
int index = bssfState.Exited(0);
Route.Add(Cities[index]);
index = bssfState.Exited(bssfState.Exited(0));
while (index != bssfState.Exited(0))
{//O(n)
Route.Add(Cities[index]);
index = bssfState.Exited(index);
}
}
else
{
Route = greedyRoute;
}
timer.Stop();
bAndBTime = timer.Elapsed;
this.count = bssfState.Cost();
// update the cost of the tour.
timer.Reset();
return Route;
}
/////////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////// BB Algorithm ////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////////////
#region MainBBAlgorithm
/// <summary>
/// performs a Branch and Bound search of the state space of partial tours
/// stops when time limit expires and uses BSSF as solution
/// Time Complexity: O((n^2)*(2^n) as that is the most dominant factor in the code, and it is a result
/// of the loop, for more details scroll to the comment above the loop in the function.
/// Space Complexity: O((n^2)*(2^n) as that is the most dominant factor in the code, and it is a result
/// of the loop, for more details scroll to the comment above the loop in the function.
/// </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];
// Helper variables
/* This part of the code takes O(1) space and time as we are just initializing some data */
int numOfCitiesLeft = Cities.Length;
int numOfSolutions = 0;
int numOfStatesCreated = 0;
int numOfStatesNotExpanded = 0;
// Initialize the time variable to stop after the time limit, which is defaulted to 60 seconds
/* This part of the code takes O(1) space and time as we are just initializing some data */
DateTime start = DateTime.Now;
DateTime end = start.AddSeconds(time_limit/1000);
// Create the initial root State and set its priority to its lower bound as we don't have any extra info at this point
/* This part of the code takes O(n^2) space and time as explained above */
State initialState = createInitialState();
numOfStatesCreated++;
initialState.setPriority(calculateKey(numOfCitiesLeft - 1, initialState.getLowerBound()));
// Create the initial BSSF Greedily
/* This part of the code takes O(n^2) time and O(n) space as explained above */
double BSSFBOUND = createGreedyInitialBSSF();
// Create the queue and add the initial state to it, then subtract the number of cities left
/* This part of the code takes O(1) time since we are just creating a data structure and
O(1,000,000) space which is just a constant so O(1) space as well*/
PriorityQueueHeap queue = new PriorityQueueHeap();
queue.makeQueue(Cities.Length);
queue.insert(initialState);
// Branch and Bound until the queue is empty, we have exceeded the time limit, or we found the optimal solution
/* This loop will have a iterate 2^n times approximately with expanding and pruning for each state, then for each state it
does O(n^2) work by reducing the matrix, so over all O((n^2)*(2^n)) time and space as well as it creates a nxn
matrix for each state*/
while (!queue.isEmpty() && DateTime.Now < end && queue.getMinLB() != BSSFBOUND)
{
// Grab the next state in the queue
State currState = queue.deleteMin();
// check if lower bound is less than the BSSF, else prune it
if (currState.getLowerBound() < BSSFBOUND)
{
// Branch and create the child states
for (int i = 0; i < Cities.Length; i++)
{
// First check that we haven't exceeded the time limit
if (DateTime.Now >= end)
break;
// Make sure we are only checking cities that we haven't checked already
if (currState.getPath().Contains(Cities[i]))
continue;
// Create the State
double[,] oldCostMatrix = currState.getCostMatrix();
double[,] newCostMatrix = new double[Cities.Length, Cities.Length];
// Copy the old array in the new one to modify the new without affecting the old
for (int k = 0; k < Cities.Length; k++)
{
for (int l = 0; l < Cities.Length; l++)
{
newCostMatrix[k, l] = oldCostMatrix[k, l];
}
}
City lastCityinCurrState = (City)currState.getPath()[currState.getPath().Count-1];
double oldLB = currState.getLowerBound();
setUpMatrix(ref newCostMatrix, Array.IndexOf(Cities, lastCityinCurrState), i, ref oldLB);
double newLB = oldLB + reduceMatrix(ref newCostMatrix);
ArrayList oldPath = currState.getPath();
ArrayList newPath = new ArrayList();
foreach (City c in oldPath)
{
newPath.Add(c);
}
newPath.Add(Cities[i]);
State childState = new State(ref newPath, ref newLB, ref newCostMatrix, Cities.Length);
numOfStatesCreated++;
// Prune States larger than the BSSF
if (childState.getLowerBound() < BSSFBOUND)
{
City firstCity = (City)childState.getPath()[0];
City lastCity = (City)childState.getPath()[childState.getPath().Count-1];
double costToLoopBack = lastCity.costToGetTo(firstCity);
// If we found a solution and it goes back from last city to first city
if (childState.getPath().Count == Cities.Length && costToLoopBack != double.MaxValue)
{
childState.setLowerBound(childState.getLowerBound() + costToLoopBack);
bssf = new TSPSolution(childState.getPath());
BSSFBOUND = bssf.costOfRoute();
numOfSolutions++;
numOfStatesNotExpanded++; // this state is not expanded because it is not put on the queue
}
else
{
// Set the priority for the state and add the new state to the queue
numOfCitiesLeft = Cities.Length - childState.getPath().Count;
childState.setPriority(calculateKey(numOfCitiesLeft, childState.getLowerBound()));
queue.insert(childState);
}
}
else
{
numOfStatesNotExpanded++; // States that are pruned are not expanded
}
}
}
currState = null;
}
numOfStatesNotExpanded += queue.getSize(); // if the code terminated before queue is empty, then those states never got expanded
Console.WriteLine("Number of states generated: " + numOfStatesCreated);
Console.WriteLine("Number of states not Expanded: " + numOfStatesNotExpanded);
Console.WriteLine("Max Number of states put in queue: " + queue.getMaxNumOfItems());
end = DateTime.Now;
TimeSpan diff = end - start;
double seconds = diff.TotalSeconds;
results[COST] = System.Convert.ToString(bssf.costOfRoute()); // load results into array here, replacing these dummy values
results[TIME] = System.Convert.ToString(seconds);
results[COUNT] = System.Convert.ToString(numOfSolutions);
return results;
}
