Random Numbers, Games, and Simulation - Advanced Topics in Java: Core Concepts in Data Structures - page 179

Suppose the customer at the head of the queue arrives at arriveTime . He will go to the first free counter. Counter
c is free if the customer arrives after the last one has left counter c , that is, if arriveTime is greater than or equal to
depart[c] . If no counter is free, he must wait. He will go to the counter that will become free first, that is, the one
with the lowest value in the array depart ; suppose this is depart[m] . He will begin service at a time that is the later of
arriveTime and depart[m] .
The program begins by asking for the number of counters and the number of customers to be simulated.
The simulation starts from time 0 , and all times are relative to this. The details are shown in Program P6.6.
Program P6.6
import java.util.*;
public class SimulateQueue {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.printf("\nHow many counters? ");
int numCounters = in.nextInt();
System.out.printf("\nHow many customers? ");
int numCustomers = in.nextInt();
doSimulation(numCounters, numCustomers);
} //end main
public static void doSimulation(int counters, int customers) {
int m, arriveTime, startServe, serveTime, waitTime;
int[] depart = new int[counters + 1];
for (int h = 1; h <= counters; h++) depart[h] = 0;
System.out.printf("\n Start Service Wait\n");
System.out.printf("Customer Arrives Service Counter Time Departs Time\n\n");
arriveTime = 0;
for (int h = 1; h <= customers; h++) {
arriveTime += random(1, 5);
m = smallest(depart, 1, counters);
startServe = Math.max(arriveTime, depart[m]);
serveTime = random(3, 10);
depart[m] = startServe + serveTime;
waitTime = startServe - arriveTime;
System.out.printf("%5d %8d %7d %6d %7d %8d %5d\n",
h, arriveTime, startServe, m, serveTime, depart[m], waitTime);
} //end for h
} //end doSimulation
public static int smallest(int list[], int lo, int hi) {
//returns the subscript of the smallest value from list[lo..hi]
int h, k = lo;
for (h = lo + 1; h <= hi; h++)
if (list[h] < list[k]) k = h;
return k;
}