SimpleDiGraph.java

package bsearch.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;
import java.util.Set;

/* TODO: This class needs more functionality, and needs tested.
 */
public class SimpleDiGraph<T> {
	List<T> vertices;
	HashMap<T,Set<T>> edges;
	
	private SimpleDiGraph()
	{
		vertices = new LinkedList<T>();
		edges = new HashMap<T,Set<T>>();
	}
	
	public Set<T> neighbors(T node)
	{
		if (edges.containsKey(node))
		{
			return edges.get(node);
		}
		else
		{
			throw new IllegalStateException("node key not found"); 
		}
	}

	
	public static SimpleDiGraph<String> readEdgeListFromFile(String filename) throws FileNotFoundException
	{
		SimpleDiGraph<String> G = new SimpleDiGraph<String>();
		
		Scanner scanner = new Scanner(new File(filename));
		
		while (scanner.hasNext())
		{
			String line = scanner.nextLine();
			String[] lineItems = line.trim().split("\\W");
			G.vertices.add(lineItems[0]);
			G.vertices.add(lineItems[1]);
			if (!G.edges.containsKey(lineItems[0]))
			{
				G.edges.put(lineItems[0], new LinkedHashSet<String>());
			}
			if (!G.edges.containsKey(lineItems[1]))
			{
				G.edges.put(lineItems[1], new LinkedHashSet<String>());
			}
			G.edges.get(lineItems[0]).add(lineItems[1]);
		}
		
		return G;
	}
	

}