Question

I have to implement a search algorithm for a school assignment. Right now, i’m having problems with sole java implementation. Here’s the code i have at the moment (i have been basing myself in some code i found here in stackoverflow for the dfs search, then i have to add verifications to meet the project criteria):

import java.util.*;

public class dfs<Grafo> {

public static void main(String[] args) {

    class Grafo{
         private Map<Integer, LinkedHashSet<Integer>> map = new HashMap();

         public void addEdge(int source, int destiny) {
                LinkedHashSet<Integer> adjacente = map.get(source);
                if(adjacente==null) {
                    adjacente = new LinkedHashSet();
                    map.put(source, adjacente);
                }
                adjacente.add(destiny);
            }

            public void addLink(int source, int destiny) {
                addEdge(source, destiny);
                addEdge(destiny, source);
            }

            public LinkedList<Integer> adjacentNodes(int last) {
                LinkedHashSet<Integer> adjacente = map.get(last);
                if(adjacente==null) {
                    return new LinkedList();
                }
                return new LinkedList<Integer>(adjacente);
            }
    }

    Scanner input = new Scanner(System.in);

    int numVertices = input.nextInt();
    int numLinks = input.nextInt();
    int startNode = input.nextInt();
    int endNode = startNode;

    Grafo mapa = new Grafo();

    for(int i = 0; i<numLinks; i++){
        mapa.addLink(input.nextInt(), input.nextInt());
    }

    List<ArrayList<Integer>> paths = new ArrayList<ArrayList<Integer>>();
    Integer currentNode = startNode;
    List<Integer> visited = new ArrayList<Integer>();
    visited.add(startNode);
    new dfs().findAllPaths(mapa, visited, paths, currentNode);

    for(ArrayList<Integer> path : paths){
        for (Integer node : path) {
            System.out.print(node);
            System.out.print(" ");
        }
        System.out.println();
}

}

private void findAllPaths(Grafo mapa, List<Integer> visited,
        List<ArrayList<Integer>> paths, Integer currentNode) {

    if (currentNode.equals(startNode)) { 
        paths.add(new ArrayList(Arrays.asList(visited.toArray())));
        return;
    }

    else {
        LinkedList<Integer> nodes = mapa.adjacentNodes(currentNode);    
        for (Integer node : nodes) {
            if (visited.contains(node)) {
                continue;
            } 
            List<Integer> temp = new ArrayList<Integer>();
            temp.addAll(visited);
            temp.add(node);          
            findAllPaths(mapa, temp, paths, node);
        }
    }

} 

}

The problem i have with this, is that i can only turn in a single java file, so i’m putting everything in this single file.
When i get to the findAllPaths function he does not recognise the “startNode” constant (eclipse says that it cannot be be resolved to a variable) and he says “adjacentNodes” function is not defined for the type Grafo.

Is there anyway i can solve this problem or do i have to rethink the way i’m doing this, if so, what’s a good way to implement this?

Answer 1

Others seem to have addressed some of your coding issues, so I just wanted to illustrate how to work with the single file constraint.

Suppose you had 3 classes, Edge, Node, and Graph that you developed in three separate files. Here’s how you could combine them:

// in file GraphSearchHomework.java
public class GraphSearchHomework {
  public static class Edge {
    // ... Edge code here ...
    // You can reference Nodes and Graphs
    // just as if this was in a separate file
  }

  public static class Node {
    // ... Node code here ...
    // You can reference Edges and Graphs
    // just as if this was in a separate file
  }

  public static class Graph {
    // ... Graph code here ...
    // You can reference Edges and Nodes
    // just as if this was in a separate file
  }

  public static void main(String args[]) {
    // This main can instantiate Graphs, Nodes, Edges
    // Keep this simple, though. Most code belongs outside of main.
  }
}

You seem to have made some mistakes trying to force this into one file. If it helps you, go ahead and develop each class separately and then combine them.