Simulation Simplified
8. Breadth-First Search
Class P2Pedia01

import edu.rit.util.Random;
import edu.rit.util.RandomSubset;
import java.util.Arrays;
import java.util.LinkedList;
public class P2Pedia01
   {
   public static void main
      (String[] args)
      throws Exception
      {
      if (args.length != 4) usage();
      int N = Integer.parseInt (args[0]);
      int K = Integer.parseInt (args[1]);
      int T = Integer.parseInt (args[2]);
      long seed = Long.parseLong (args[3]);
      Random prng = Random.getInstance (seed);
      int[][] conn = new int[N][K+1];
      for (int i = 0; i < N; ++ i) conn[i][0] = (i + 1)%N;
      int[] dist = new int[N];
      int sumPathLength = 0;
      for (int trial = 0; trial < T; ++ trial)
         {
         for (int i = 0; i < N; ++ i)
            {
            RandomSubset rs = new RandomSubset (prng, N)
               .remove (i) .remove ((i + 1)%N);
            for (int j = 1; j <= K; ++ j) conn[i][j] = rs.next();
            }
         int orig = prng.nextInt (N);
         int match = prng.nextInt (N);
         int len = shortestPathLength (conn, dist, orig, match);
         sumPathLength += len;
         System.out.printf ("Trial %d%n", trial);
         System.out.printf ("  Node  Connected to nodes%n");
         for (int i = 0; i < N; ++ i)
            {
            System.out.printf ("  %-4d", i);
            for (int j = 0; j <= K; ++ j)
               {
               System.out.printf ("  %d", conn[i][j]);
               }
            System.out.println();
            }
         System.out.printf ("  Originating node = %d%n", orig);
         System.out.printf ("  Matching node = %d%n", match);
         System.out.printf ("  Query path length = %d%n", len);
         }
      System.out.printf ("Average query path length = %.2f%n",
         ((double) sumPathLength)/((double) T));
      }

   private static int shortestPathLength
      (int[][] conn,
       int[] dist,
       int orig,
       int match)
      {
      if (orig == match) return 0;
      Arrays.fill (dist, -1);
      dist[orig] = 0;
      LinkedList<Integer> queue = new LinkedList<Integer>();
      queue.addLast (orig);
      for (;;)
         {
         int i = queue.removeFirst();
         for (int j : conn[i])
            {
            if (j == match)
               {
               return dist[i] + 1;
               }
            else if (dist[j] == -1)
               {
               dist[j] = dist[i] + 1;
               queue.addLast (j);
               }
            }
         }
      }

   private static void usage()
      {
      System.err.println
         ("Usage: java P2Pedia01 <N> <K> <T> <seed>");
      System.exit (1);
      }
   }