#include <stdio.h>
#include <stdlib.h>

#define numOfMinutes 100

struct RecType {
		int info;
		struct RecType *next;
		};
typedef struct RecType *PtrType;

PtrType Q = NULL, QTail = NULL;

empty()
{
    return Q == NULL;
}

void
enq(int t)
{   PtrType tmp = (PtrType) malloc(sizeof(struct RecType));

    tmp->info = t;
    tmp->next = NULL;
    if (!Q)
	 Q = QTail = tmp;
    else {
	 QTail->next = tmp;
	 QTail = tmp;
    }
}

deq()
{   PtrType tmp = Q;
    int t;

    Q = Q->next;
    t = tmp->info;
    free(tmp);
    return t;
}

float
ScanQ()
{   PtrType tmp = Q;
    int WaitingTime;

    for (WaitingTime = 0; tmp; WaitingTime += tmp->info, tmp = tmp->next);
    return WaitingTime/60.0;
}

int
option(int percents[])
{   register int i, choice = random(100)+1, perc;

    for (perc = percents[0], i = 0; perc < choice; perc += percents[i+1], i++);
    return i;
}

main()
{   int arrivals[] = {15,20,25,10,30};
    int service[] = {0,0,0,10,5,10,10,0,15,25,10,15};
    int clerks[] = {0,0,0,0,0}, clerkssize = sizeof(clerks)/sizeof(int);
    int j, customers, t, i, thereIsLine = 0;
    float maxWait = 0.0, currWait = 0.0;

    for (t = 1; t <= numOfMinutes; t++) {
	printf("t = %d ",t);
	for (i = 0; i < clerkssize; i++)/* after each minute subtract       */
	    if (clerks[i] < 60)		/* at most 60 seconds from time     */
		 clerks[i] = 0;		/* left to service the current      */
	    else clerks[i] -= 60;	/* customer by clerk i; 	    */
	customers = option(arrivals);
	for (i = 0; i < customers; i++) /* enq all new customers (or rather */
	    enq(option(service)*10);	/* service time they require);      */
	for (i = 0; i < clerkssize && !empty(); ) /* deq customers  	    */
	    if (clerks[i] < 60)		/* when clerks are available; 	    */
		 clerks[i] += deq();	/* assign more than one customer    */
	    else i++;			/* to a clerk if service time 	    */
					/* is still below 60 sec; 	    */
	if (!empty(Q)) {
	    thereIsLine++;
	    currWait = ScanQ();
	    if (maxWait < currWait)
		maxWait = currWait;
	}
    }
    printf("\nFor %d clerks, there was a line %.1f%% of the time;\n",
	clerkssize,(float)thereIsLine/numOfMinutes*100.0);
    printf("maximum wait time was %.1f min.\n",maxWait);
}