算法Sedgewick第四版-第1章基础-024-M/M/1 queue

 /******************************************************************************
  *  Compilation:  javac MM1Queue.java
  *  Execution:    java MM1Queue lambda mu
  *  Dependencies: Queue.java Histogram.java
  *
  *  Simulate an M/M/1 queue where arrivals and departures are Poisson
  *  processes with arrival rate lambda and service rate mu.
  *
  *  % java MM1Queue .20 .33
  *
  *  % java MM1Queue .20 .25
  *
  *  % java MM1Queue .20 .21
  *
  *
  *  Remarks
  *  -------
  *   - We assume the interrarrival and service times are independent.
  *
  *
  ******************************************************************************/

 public class MM1Queue { 

     public static void main(String[] args) {
         double lambda = Double.parseDouble(args[0]);  // arrival rate
         double mu     = Double.parseDouble(args[1]);  // service rate

         Queue<Double> q = new Queue<Double>();            // arrival times of customers
         double nextArrival   = StdRandom.exp(lambda);     // time of next arrival
         double nextDeparture = Double.POSITIVE_INFINITY;  // time of next departure

         // histogram object
         Histogram hist = new Histogram(60);

         // simulate an M/M/1 queue
         while (true) {

             // it's an arrival
             if (nextArrival <= nextDeparture) {
                 if (q.isEmpty()) nextDeparture = nextArrival + StdRandom.exp(mu);
                 q.enqueue(nextArrival);
                 nextArrival += StdRandom.exp(lambda);
             }

             // it's a departure
             else {
                 double wait = nextDeparture - q.dequeue();
                 StdOut.printf("Wait = %6.2f, queue size = %d\n", wait, q.size());
                 hist.addDataPoint(Math.min(60,  (int) (Math.round(wait))));
                 hist.draw();
                 if (q.isEmpty()) nextDeparture = Double.POSITIVE_INFINITY;
                 else             nextDeparture += StdRandom.exp(mu);

             }
         }

     }

 }