UndirectedGraphs.java

package algorithms;

import java.util.*;


/**
 * Implementation of undirected graph represented using adjacency list.
 * 
 * @author joeytawadrous
 */
public final class UndirectedGraphs<T> implements Iterable<T>
{
    private final Map<T, Set<T>> graph = new HashMap<T, Set<T>>();
 
    public boolean addNode(T node) 
    {
    	if (graph.containsKey(node)) { return false; }
 
    	graph.put(node, new HashSet<T>());
     
    	return true;
    }
 
    public void addEdge(T start, T dest) 
    {
    	if (!graph.containsKey(start) || !graph.containsKey(dest))
    	{
    		System.out.println("No such nodes in the graph."); 
    	}
    	else
    	{
    		graph.get(start).add(dest);
    		graph.get(dest).add(start);
    	}
    }
    
    public void removeEdge(T start, T dest) 
    {
    	if (!graph.containsKey(start) || !graph.containsKey(dest))
    	{
    		System.out.println("No such nodes in the graph."); 
    	}
    	else
    	{
    		graph.get(start).remove(dest);
    		graph.get(dest).remove(start);
    	}	
    }
 
    public boolean isEdgeExists(T start, T end) 
    {
    	if (!graph.containsKey(start) || !graph.containsKey(end))
    	{
    		System.out.println("No such nodes in the graph."); 
    	}
 
    	return graph.get(start).contains(end);
    }
 
    public Set<T> getNeighbors(T node) 
    {
    	Set<T> neighbors = graph.get(node);
    	
    	if (neighbors == null)
    	{
    		System.out.println("No such nodes in the graph."); 
    	}
 
    	return Collections.unmodifiableSet(neighbors);
    }
 
    public Iterator<T> iterator() 
    {
    	return graph.keySet().iterator();
    }
    
    public Iterable<T> getNodes()
    {
    	return graph.keySet();
    }
    
    public int size()
    {
    	return graph.size();
    }
    
    public boolean isEmpty()
    {
    	return graph.isEmpty();
    }
}