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);

}
}

}

}