Generic Directed, Weighted Graph with Dijkstra's Shortest Path

DiGraph.java

/* Generic Directed Weighted Graph with Dijkstra's Shortest Path Algorithm
* by /u/Philboyd_Studge
* for /r/javaexamples
*/

import java.util.List;
import java.util.Queue;
import java.util.PriorityQueue;
import java.util.Deque;
import java.util.LinkedList;
import java.util.ArrayList;
import java.util.Collections;

@SuppressWarnings("unchecked")
/**
 * Creates a directed, weighted <tt>Graph</tt> for any Comparable type
 * <p> add Edge date with <code>add(T valueforVertexFrom, T valueForVertexTo, int cost)</code>
 * <p> use <code>getPath(T valueFrom, T valueTo)</code> to get the shortest path between
 * the two using Dijkstra's Algorithm
 * <p> If returned List has a size of 1 and a cost of Integer.Max_Value then no conected path
 * was found
 *
 * @author /u/Philboyd_Studge
 */
public class DiGraph<T extends Comparable<T>>
{
	public enum State { UNVISITED, VISITED, COMPLETE };

	private ArrayList<Vertex> vertices;
	private ArrayList<Edge> edges;

	/**
	 * Default Constructor
	 */
	public DiGraph()
	{
		vertices = new ArrayList<>();
		edges = new ArrayList<>();
	}

	/**
	 * Creates Edge from two values T directed from -- to
	 * @param from Value for Vertex 1
	 * @param to Value for Vertex 2
	 * @param cost Cost or weight of edge
	 */
	public void add(T from, T to, int cost)
	{
		Edge temp = findEdge(from, to);
		if (temp != null)
		{
			// Don't allow multiple edges, update cost.
			System.out.println("Edge " + from + "," + to + " already exists. Changing cost.");
			temp.cost = cost;
		}
		else
		{
			// this will also create the vertices
			Edge e = new Edge(from, to, cost);
			edges.add(e);
		}
	}

	/**
	 * find Vertex in Graph from value
	 * @param v value of type T
	 * @return Vertex, or <code>null</code> if not found.
	 */
	private Vertex findVertex(T v)
	{
		for (Vertex each : vertices)
		{
			if (each.value.compareTo(v)==0)
				return each;
		}
		return null;
	}

	/**
	 * Find edge containg two vertices
	 * in direction v1 -> v2
	 * @param v1 Vertex 'from'
	 * @param v2 Vertex 'to'
	 * @return Edge, or <code>null</code> if not found.
	 */
	private Edge findEdge(Vertex v1, Vertex v2)
	{
		for (Edge each : edges)
		{
			if (each.from.equals(v1) && each.to.equals(v2))
			{
				return each;
			}
		}
		return null;
	}

	/**
	 * Find edge from two values
	 * @param from from value of type T
	 * @param to to value of type T
	 * @return Edge, or <code>null</code> if not found.
	 */
	private Edge findEdge(T from, T to)
	{
		for (Edge each : edges)
		{
			if (each.from.value.equals(from) && each.to.value.equals(to))
			{
				return each;
			}
		}
		return null;
	}

	/**
	 * Sets all states to UNVISITED
	 */
	private void clearStates()
	{
		for (Vertex each : vertices)
		{
			each.state = State.UNVISITED;
		}
	}

	/**
	 * Test if DFS or BFS returned a connected graph
	 * @return true if connected, false if not.
	 */
	public boolean isConnected()
	{
		for (Vertex each : vertices)
		{
			if (each.state != State.COMPLETE)
				return false;
		}
		return true;
	}

	/**
	 * Performs a recursive Depth First Search on the
	 * 'root' node (the first vertex created)
	 * @return true if connected, false if empty or not connected
	 */
	public boolean DepthFirstSearch()
	{
		if (vertices.isEmpty()) return false;

		clearStates();
		// get first node
		Vertex root = vertices.get(0);
		if (root==null) return false;

		// call recursive function
		DepthFirstSearch(root);
		return isConnected();
	}

	/**
	 * Helper for Depth first search
	 * @param v vertex
	 */
	private void DepthFirstSearch(Vertex v)
	{
		v.state = State.VISITED;

		// loop through neighbors
		for (Vertex each : v.outgoing)
		{
			if (each.state ==State.UNVISITED)
			{
				DepthFirstSearch(each);
			}
		}
		v.state = State.COMPLETE;
	}

	/**
	 * Performs a Breadth-First Search
	 * starting at 'root' node (First created vertex)
	 * @return true is connected, false is not or if empty
	 */
	public boolean BreadthFirstSearch()
	{
		if (vertices.isEmpty()) return false;
		clearStates();

		Vertex root = vertices.get(0);
		if (root==null) return false;

		Queue<Vertex> queue = new LinkedList<>();
		queue.add(root);
		root.state = State.COMPLETE;

		while (!queue.isEmpty())
		{
			root = queue.peek();
			for (Vertex each : root.outgoing)
			{

				if (each.state==State.UNVISITED)
				{
					each.state = State.COMPLETE;
					queue.add(each);
				}
			}
			queue.remove();
		}
		return isConnected();
	}

	/**
	 * Perfoms a Breadth-First Search on a given starting vertex
	 * @param v1 Value of type T for starting vertex
	 * @return true if connected, false if not or if empty
	 */
	public boolean BreadthFirstSearch(T v1)
	{
		if (vertices.isEmpty()) return false;
		clearStates();

		Vertex root = findVertex(v1);
		if (root==null) return false;

		Queue<Vertex> queue = new LinkedList<>();
		queue.add(root);
		root.state = State.COMPLETE;

		while (!queue.isEmpty())
		{
			root = queue.peek();
			for (Vertex each : root.outgoing)
			{

				if (each.state==State.UNVISITED)
				{
					each.state = State.COMPLETE;
					queue.add(each);
				}
			}
			queue.remove();
		}
		return isConnected();
	}

	/**
	 * Creates path information on the graph using the Dijkstra Algorithm,
	 * Puts the information into the Vertices, based on given starting vertex.
	 * @param v1 Value of type T for starting vertex
	 * @return true if successfull, false if empty or not found.
	 */
	private boolean Dijkstra(T v1)
	{
		if (vertices.isEmpty()) return false;

		// reset all vertices minDistance and previous
		resetDistances();

		// make sure it is valid
		Vertex source = findVertex(v1);
		if (source==null) return false;

		// set to 0 and add to heap
		source.minDistance = 0;
		PriorityQueue<Vertex> pq = new PriorityQueue<>();
		pq.add(source);

		while (!pq.isEmpty())
		{
			//pull off top of queue
			Vertex u = pq.poll();

			// loop through adjacent vertices
			for (Vertex v : u.outgoing)
			{
				// get edge
				Edge e = findEdge(u, v);
				if (e==null) return false;
				// add cost to current
				int totalDistance = u.minDistance + e.cost;
				if (totalDistance < v.minDistance)
				{
					// new cost is smaller, set it and add to queue
					pq.remove(v);
					v.minDistance = totalDistance;
					// link vertex
					v.previous = u;
					pq.add(v);
				}
			}
		}
		return true;
	}

	/**
	 * Goes through the result tree created by the Dijkstra method
	 * and steps backward
	 * @param target Vertex end of path
	 * @return string List of vertices and costs
	 */
	private List<String> getShortestPath(Vertex target)
	{
		List<String> path = new ArrayList<String>();

		// check for no path found
		if (target.minDistance==Integer.MAX_VALUE)
		{
			path.add("No path found");
			return path;
		}

		// loop through the vertices from end target 
		for (Vertex v = target; v !=null; v = v.previous)
		{
			path.add(v.value + " : cost : " + v.minDistance);
		}

		// flip the list
		Collections.reverse(path);
		return path;
	}

	/**
	 * for Dijkstra, resets all the path tree fields
	 */
	private void resetDistances()
	{
		for (Vertex each : vertices)
		{
			each.minDistance = Integer.MAX_VALUE;
			each.previous = null;
		}
	}

	/**
	 * PUBLIC WRAPPER FOR PRIVATE FUNCTIONS
	 * Calls the Dijkstra method to build the path tree for the given
	 * starting vertex, then calls getShortestPath method to return
	 * a list containg all the steps in the shortest path to
	 * the destination vertex.
	 * @param from value of type T for Vertex 'from'
	 * @param to value of type T for vertex 'to'
	 * @return ArrayList of type String of the steps in the shortest path.
	 */
	public List<String> getPath(T from, T to)
	{
		boolean test = Dijkstra(from);
		if (test==false) return null;
		List<String> path = getShortestPath(findVertex(to));
		return path;
	}

	/**
	 * @return string of vertices
	 */
	@Override
	public String toString()
	{
		String retval = "";
		for (Vertex each : vertices)
		{
			retval += each.toString() + "\n";
		}
		return retval;
	}

	/**
	 * list all the edges into a string
	 * @return string of edge data
	 */
	public String edgesToString()
	{
		String retval = "";
		for (Edge each : edges)
		{
			retval += each + "\n";
		}
		return retval;
	}


	class Vertex implements Comparable<Vertex>
	{
		T value;

		// variables for Dijkstra Tree
		Vertex previous = null;
		int minDistance = Integer.MAX_VALUE;

		List<Vertex> incoming;
		List<Vertex> outgoing;
		State state;

		/**
		 * Creates new Vertex with value T
		 * @param value T
		 */
		public Vertex(T value)
		{
			this.value = value;
			incoming = new ArrayList<>();
			outgoing = new ArrayList<>();
			state = State.UNVISITED;
		}

		/**
		 * @param other Vertex to compare to
		 */
		@Override
		public int compareTo(Vertex other)
		{
			return Integer.compare(minDistance, other.minDistance);
		}

		/**
		 * Add Vertex to adjacent incoming list
		 * @param vert Vertex of incoming adjacent
		 */
		public void addIncoming(Vertex vert)
		{
			incoming.add(vert);
		}
		public void addOutgoing(Vertex vert)
		{
			outgoing.add(vert);
		}

		/**
		 * Get string of Vertex with all it's ingoing and outgoing adjacencies
		 * @ return string
		 */
		@Override
		public String toString()
		{
			String retval = "";
			retval += "Vertex: " + value + " : ";
			retval += " In: ";
			for (Vertex each : incoming) retval+= each.value + " ";
			retval += "Out: ";
			for (Vertex each : outgoing) retval += each.value + " ";
			return retval;
		}
	}

	class Edge
	{
		Vertex from;
		Vertex to;
		int cost;

		/**
		 * @param v1 value of type T for 'from' vertex
		 * @param v2 value of type T for 'to' vertex
		 * @param cost integer value for cost/weight of edge
		 */
		public Edge(T v1, T v2, int cost)
		{
			from = findVertex(v1);
			if (from == null)
			{
				from = new Vertex(v1);
				vertices.add(from);
			}
			to = findVertex(v2);
			if (to == null)
			{
				to = new Vertex(v2);
				vertices.add(to);
			}
			this.cost = cost;

			from.addOutgoing(to);
			to.addIncoming(from);
		}

		/**
		 * @return Edge as string
		 */
		@Override
		public String toString()
		{
			return "Edge From: " + from.value + " to: " + to.value + " cost: " + cost;
		}
	}
}

DiGraphTest.java

import java.util.List;
import java.util.ArrayList;

@SuppressWarnings("unchecked")
/**
 * Directed Graph Test - Dijkstra Shortest Path
 * 
 * @author /u/Philboyd_Studge
 */
public class DiGraphTest
{
	public static void main(String[] args)
	{

		// create graph
		DiGraph graph = new DiGraph();

		// add a bunch of edges
		graph.add("SACRAMENTO", "PHOENIX", 150);
		graph.add("PHOENIX", "SACRAMENTO", 135);
		graph.add("PHOENIX", "SLC", 120);
		graph.add("SLC", "SACRAMENTO", 175);
		graph.add("SACRAMENTO", "PHOENIX", 160); // edge already exists!!!
		graph.add("SACRAMENTO", "PORTLAND", 90);
		graph.add("PORTLAND", "SLC", 185);
		graph.add("OAKLAND", "SACRAMENTO", 45);
		graph.add("PORTLAND", "OAKLAND", 100);
		graph.add("SLC", "OAKLAND", 150);
		graph.add("LAX","OAKLAND", 75);
		graph.add("SLC", "LAS VEGAS", 100);
		graph.add("LAS VEGAS", "CHICAGO", 250);

		System.out.println("Graph is connected: " + graph.DepthFirstSearch());
		System.out.println("Connected from LAX:" + graph.BreadthFirstSearch("LAX"));
		System.out.println();

		System.out.println(graph);
		System.out.println(graph.edgesToString());

		System.out.println("LAX to PORTLAND");
		List<String> path = graph.getPath("LAX", "PORTLAND");
		for (String each : path) 
			System.out.println(each);

		System.out.println("\nSLC to PHOENIX");
		path = graph.getPath("SLC", "PHOENIX");
		for (String each : path) 
			System.out.println(each);

		System.out.println("Adding Edge Las Vegas to Phoenix at cost $120");
		graph.add("LAS VEGAS", "PHOENIX", 120);

		System.out.println("\nSLC to PHOENIX");
		path = graph.getPath("SLC", "PHOENIX");
		for (String each : path) 
			System.out.println(each);

		System.out.println("\nSACRAMENTO to LAX");
		path = graph.getPath("SACRAMENTO", "LAX");
		for (String each : path) 
			System.out.println(each);

		System.out.println("\nSACRAMENTO to CHICAGO");
		path = graph.getPath("SACRAMENTO", "CHICAGO");
		for (String each : path) 
			System.out.println(each);
	}
}

how can i break self loop? i.e., roads connecting the same pair of vertex

Is it possible for this to be edited to also find the road backwards from a city. For example:

SACRAMENTO to LAS VEGAS
SACRAMENTO : cost : 0
PORTLAND : cost : 90
SLC : cost : 275
LAS VEGAS : cost : 375

Currently it cannot find the way back:

LAS VEGAS to SACRAMENTO
No path found

Is it possible for this to be edited to also find the road backwards from a city. For example:

SACRAMENTO to LAS VEGAS
SACRAMENTO : cost : 0
PORTLAND : cost : 90
SLC : cost : 275
LAS VEGAS : cost : 375

Currently it cannot find the way back:

LAS VEGAS to SACRAMENTO
No path found

Use an Undirected graph instead of Directed - to do this simply just add every edge in both directions. So you could add 'SACRAMENTO, PHOENIX, 160" and "PHOENIX, SACRAMENTO, 160"