I'm trying to modify Dijkstra's algorithm to show all the paths that have the minimum value. So I decided to use a list of previous vertices. And I added an if clause that checks if the path is igual to the previous with minimum value I add the previous vertex as the parent of the current one. The problem is that I am getting a StackOverflow error and I don't know what is causing it. This is my code: The purpose of the code below is to calculate Dijkstra for all of the vertices in the graph, calculate the number of times a vertex appears in the minimum paths found and display in decrescent order the all of them.
public class Dijkstra {
public static final Map<String, Integer> ordem = new HashMap<>();
public static void main(String[] args) throws FileNotFoundException, IOException {
List<Graph.Edge> edges = new ArrayList<>();
try {
FileReader arq = new FileReader("input.txt");
BufferedReader fw = new BufferedReader(arq);
String linha = "";
while (fw.ready()) {
linha = fw.readLine();
if (!linha.equals("0,0,0")) {
String parts[] = linha.split(",");
ordem.put(parts[0], 0);
ordem.put(parts[1], 0);
Graph.Edge a = new Graph.Edge(parts[0], parts[1], 100 - Integer.parseInt(parts[2]));
edges.add(a);
} else {
break;
}
}
fw.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
Graph g = new Graph(edges);
for (int i = 0; i < 5; i++) {
g.dijkstra(String.valueOf(i));
g.printAllPaths();
}
Object[] a = ordem.entrySet().toArray();
Arrays.sort(a, new Comparator() {
public int compare(Object o1, Object o2) {
return ((Map.Entry<String, Integer>) o2).getValue()
.compareTo(((Map.Entry<String, Integer>) o1).getValue());
}
});
for (Object e : a) {
System.out.print(((Map.Entry<String, Integer>) e).getKey() + " ");
}
System.out.println("\n");
}
}
class Graph {
private final Map<String, Vertex> graph;
public static class Edge {
public final String v1, v2;
public final int dist;
public Edge(String v1, String v2, int dist) {
this.v1 = v1;
this.v2 = v2;
this.dist = dist;
}
}
public static class Vertex implements Comparable<Vertex> {
public final String name;
public int dist = Integer.MAX_VALUE;
public List<Vertex> previous = new ArrayList<>();
public final Map<Vertex, Integer> neighbours = new HashMap<>();
public Vertex(String name) {
this.name = name;
}
private void printPath() {
if (this == this.previous) {
} else if (this.previous == null) {
} else {
//This is where I am getting the error
for (int i = 0; i<this.previous.size(); i++){
this.previous.get(i).printPath();
Dijkstra.ordem.replace(this.name, Dijkstra.ordem.get(this.name) + 1);
}
}
}
public int compareTo(Vertex other) {
if (dist == other.dist) {
return name.compareTo(other.name);
}
return Integer.compare(dist, other.dist);
}
@Override
public String toString() {
return "(" + name + ", " + dist + ")";
}
}
public Graph(List<Graph.Edge> edges) {
graph = new HashMap<>(edges.size());
for (Edge e : edges) {
if (!graph.containsKey(e.v1)) {
graph.put(e.v1, new Vertex(e.v1));
}
if (!graph.containsKey(e.v2)) {
graph.put(e.v2, new Vertex(e.v2));
}
}
for (Edge e : edges) {
graph.get(e.v1).neighbours.put(graph.get(e.v2), e.dist);
graph.get(e.v2).neighbours.put(graph.get(e.v1), e.dist);
}
}
public void dijkstra(String startName) {
if (!graph.containsKey(startName)) {
System.err.printf("Graph doesn't contain start vertex \"%s\"\n", startName);
return;
}
final Vertex source = graph.get(startName);
NavigableSet<Vertex> q = new TreeSet<>();
// Inicializacao dos vertices
for (Vertex v : graph.values()) {
//v.previous = v == source ? list : null;
if (v == source) {
v.previous.add(source);
} else {
v.previous = new ArrayList<>();
}
v.dist = v == source ? 0 : Integer.MAX_VALUE;
q.add(v);
}
dijkstra(q);
}
private void dijkstra(final NavigableSet<Vertex> q) {
Vertex u, v;
while (!q.isEmpty()) {
u = q.pollFirst();
if (u.dist == Integer.MAX_VALUE) {
}
for (Map.Entry<Vertex, Integer> a : u.neighbours.entrySet()) {
v = a.getKey();
final int alternateDist = u.dist + a.getValue();
if (alternateDist < v.dist) {
q.remove(v);
v.dist = alternateDist;
v.previous.add(u);
q.add(v);
} else if(alternateDist == v.dist) {
v.previous.add(u);
}
}
}
}
public void printPath(String endName) {
if (!graph.containsKey(endName)) {
System.err.printf("Graph doesn't contain end vertex \"%s\"\n", endName);
return;
}
graph.get(endName).printPath();
//System.out.println();
}
public void printAllPaths() {
for (Vertex v : graph.values()) {
v.printPath();
}
}
}
This is the error:
Exception in thread "main" java.lang.StackOverflowError
at Graph$Vertex.printPath(Dijkstra.java:117)
at Graph$Vertex.printPath(Dijkstra.java:118)
