content: /*************************************************************************
   *  Compilation:  javac Graph.java        
   *  Execution:    java Graph input.txt
   *  Dependencies: Bag.java In.java StdOut.java
   *  Data files:   http://algs4.cs.princeton.edu/41undirected/tinyG.txt
   *
   *  A graph, implemented using an array of sets.
   *  Parallel edges and self-loops allowed.
   *
   *  % java Graph tinyG.txt
   *  13 vertices, 13 edges 
   *  0: 6 2 1 5 
   *  1: 0 
   *  2: 0 
   *  3: 5 4 
   *  4: 5 6 3 
   *  5: 3 4 0 
   *  6: 0 4 
   *  7: 8 
   *  8: 7 
   *  9: 11 10 12 
   *  10: 9 
   *  11: 9 12 
   *  12: 11 9 
   *
   *  % java Graph mediumG.txt
   *  250 vertices, 1273 edges 
   *  0: 225 222 211 209 204 202 191 176 163 160 149 114 97 80 68 59 58 49 44 24 15 
   *  1: 220 203 200 194 189 164 150 130 107 72 
   *  2: 141 110 108 86 79 51 42 18 14 
   *  ...
   *  
   *************************************************************************/
  
  
  /**
   *  The <tt>Graph</tt> class represents an undirected graph of vertices
   *  named 0 through V-1.
   *  It supports the following operations: add an edge to the graph,
   *  iterate over all of the neighbors adjacent to a vertex.
   *  Parallel edges and self-loops are permitted.
   *  <p>
   *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/51undirected">Section 5.1</a> of
   *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
   */
  public class Graph {
      private final int V;
      private int E;
      private Bag<Integer>[] adj;
      
     /**
       * Create an empty graph with V vertices.
       */
      public Graph(int V) {
          if (V < 0) throw new RuntimeException("Number of vertices must be nonnegative");
          this.V = V;
          this.E = 0;
          adj = (Bag<Integer>[]) new Bag[V];
          for (int v = 0; v < V; v++) {
              adj[v] = new Bag<Integer>();
          }
      }
  
     /**
       * Create a random graph with V vertices and E edges.
       * Expected running time is proportional to V + E.
       */
      public Graph(int V, int E) {
          this(V);
          if (E < 0) throw new RuntimeException("Number of edges must be nonnegative");
          for (int i = 0; i < E; i++) {
              int v = (int) (Math.random() * V);
              int w = (int) (Math.random() * V);
              addEdge(v, w);
          }
      }
  
     /**  
       * Create a digraph from input stream.
       */
      public Graph(In in) {
          this(in.readInt());
          int E = in.readInt();
          for (int i = 0; i < E; i++) {
              int v = in.readInt();
              int w = in.readInt();
              addEdge(v, w);
          }
      }
  
     /**
       * Copy constructor.
       */
      public Graph(Graph G) {
          this(G.V());
          this.E = G.E();
          for (int v = 0; v < G.V(); v++) {
              // reverse so that adjacency list is in same order as original
              Stack<Integer> reverse = new Stack<Integer>();
              for (int w : G.adj[v]) {
                  reverse.push(w);
              }
              for (int w : reverse) {
                  adj[v].add(w);
              }
          }
      }
  
     /**
       * Return the number of vertices in the graph.
       */
      public int V() { return V; }
  
     /**
       * Return the number of edges in the graph.
       */
      public int E() { return E; }
  
  
     /**
       * Add the edge v-w to graph.
       */
      public void addEdge(int v, int w) {
          E++;
          adj[v].add(w);
          adj[w].add(v);
      }
  
  
     /**
       * Return the list of neighbors of vertex v as in Iterable.
       */
      public Iterable<Integer> adj(int v) {
          return adj[v];
      }
  
  
     /**
       * Return a string representation of the graph.
       */
      public String toString() {
          StringBuilder s = new StringBuilder();
          String NEWLINE = System.getProperty("line.separator");
          s.append(V + " vertices, " + E + " edges " + NEWLINE);
          for (int v = 0; v < V; v++) {
              s.append(v + ": ");
              for (int w : adj[v]) {
                  s.append(w + " ");
              }
              s.append(NEWLINE);
          }
          return s.toString();
      }
  
  
     /**
       * Test client.
       */
      public static void main(String[] args) {
          In in = new In(args[0]);
          Graph G = new Graph(in);
          StdOut.println(G);
      }
  
  }
  