package graphs.digraphs;
import java.util.Set;
import java.util.HashSet;

/**
 *  DiGraph class represents an directed graph of vertices named 0 through V-1.
 *  Parallel edges and self-loops are permitted.
 */
public class DiGraph {
	
	 private final int numV;
	 private int numE;
	 private Set<Integer>[] adjacents;
	    
	 /**
	  * Create an empty digraph with V vertices.
	  */
	 public DiGraph(int v) {
		 if (v < 0) 
			 throw new RuntimeException("Number of vertices must be nonnegative");
		 this.numV = v;
		 this.numE = 0;
		 adjacents = (Set<Integer>[]) new Set[numV];
		 for (int i = 0; i < v; i++) {
			 adjacents[i] = new HashSet<Integer>();
		 }
	 }

	 /**
	  * Return the number of vertices in the digraph.
	  */
	 public int numberOfVerteces() {
		 return numV;
	 }

	/**
	 * Return the number of edges in the digraph.
	 */
	 public int numberOfEdges() {
		 return numE;
	 }

	 /**
	  * Add the directed edge v-w to the digraph.
	  */
	 public void addEdge(int v, int w) {
		 adjacents[v].add(w);
		 numE++;
	 }

	 /**
	  * Return the list of neighbors of vertex v as in Iterable.
	  */
	 public Iterable<Integer> adjacents(int v) {
		 return adjacents[v];
	 }

	 /**
	  * Return a string representation of the digraph.
	  */
	 public String toString() {
		 StringBuilder s = new StringBuilder();
		 //String NEWLINE = System.getProperty("line.separator");
		 s.append(numV + " " + numE + "\n");
		 for (int i = 0; i < numV; i++) {
			 s.append(i + ": ");
			 for (int w : adjacents[i]) {
				 s.append(w + " ");
			 }
			 s.append("\n");
		 }
		 return s.toString();
	 }

}