/**
* Method to find the Euler Tour based on the Hierholzer's algorithm.
*
* @param g : Input graph for which the tour is to be found.
* @return : Returns a list of edges that comprises of the Euler Tour.
*/
public static List<Edge> findEulerTour(Graph<Vertex> g) {
Vertex start = g.verts.get(1);
Stack<Edge> forward = new Stack<Edge>();
Stack<Edge> backtrack = new Stack<Edge>();
Edge e = getUnvisitedEdge(start);
while (e != null) {
e.visited = true;
forward.push(e);
e = getUnvisitedEdge(e.To);
}
while (!(forward.isEmpty())) {
e = forward.pop();
backtrack.push(e);
e = getUnvisitedEdge(e.From);
while (e != null) {
e.visited = true;
forward.push(e);
e = getUnvisitedEdge(e.To);
}
}
List<Edge> path = new LinkedList<Edge>();
while (!backtrack.isEmpty()) {
Edge edge = backtrack.pop();
path.add(edge);
}
return path;
}
/**
* Method to return the unvisited edge for the Graph
*
* @param n : Input vertex for which the unvisited Edges are to be determined.
* @return : Returns the unvisited Edges for the input Vertex.
*/
public static Edge getUnvisitedEdge(Vertex n) {
for (Edge e : n.Adj) {
if (e.visited == false && e.From.equals(n)) {
e.visited = true;
return e;
}
}
return null;
}
/**
* Utility Method to determine if the Vertex has unvisited children
*
* @param n : Input vertex for which the children are to be determined.
* @return : Returns the unvisited child Vertex for the input Vertex.
*/
public static Vertex getUnvisitedChildren(Vertex n) {
for (Edge e : n.Adj) {
if (e.visited == false && e.From.equals(n)) {
e.visited = true;
return e.To;
}
}
return null;
}
/**
* Method to verify if the Input tour is a valid tour.
*
* @param g : Input graph for which the tour is to be verified.
* @param tour : The tour output provided by findEulerTour() method.
* @param start : The start vertex from where the tour begins.
* @return : Returns true if tour is valid or false if the tour is rejected.
*/
static boolean verifyTour(Graph<Vertex> g, List<Edge> tour, Vertex start) {
Edge ePrevious = null;
boolean previousHead = true;
int count = 0;
System.out.println("Size " + g.verts.size());
for (Edge e : tour) {
e.To.seen = false;
e.From.seen = false;
e.visited = false;
}
for (Edge e : tour) {
count++;
if (count == 2) {
if (ePrevious.From.name == e.From.name || ePrevious.To.name == e.From.name) {
previousHead = false;
System.out.println("01");
} else if (ePrevious.To.name == e.To.name || ePrevious.From.name == e.To.name) {
previousHead = true;
System.out.println("02");
} else {
System.out.println("03" + count);
System.out.println(ePrevious.To.name);
System.out.println(e.From.name);
return false;
}
} else if (previousHead && ePrevious != null && count > 2) {
if (ePrevious.From.name == e.From.name) {
previousHead = false;
System.out.println("1");
} else if (ePrevious.From.name == e.To.name) {
previousHead = true;
System.out.println("2");
} else {
System.out.println("3" + count);
return false;
}
} else if (!previousHead && ePrevious != null && count > 2) {
if (ePrevious.To.name == e.From.name) {
System.out.println("4");
previousHead = false;
} else if (ePrevious.To.name == e.To.name) {
System.out.println("5");
previousHead = true;
} else {
System.out.println("6" + count);
return false;
}
}
e.From.seen = true;
e.To.seen = true;
if (e.visited) {
System.out.println("Edge is visited twice");
return false;
} else {
e.visited = true;
}
ePrevious = e;
}
Iterator<Vertex> iterator = g.iterator();
Vertex vertex;
while (iterator.hasNext()) /*
* declaring the vertices as not yet
* processed
*/ {
vertex = (Vertex) iterator.next();
if (!vertex.seen) {
System.out.println("9");
return false;
}
for (Edge edge : vertex.Adj) {
if (!edge.visited) {
System.out.println("10");
return false;
}
}
}
return true;
}