Unfair service centre simulation

Data structure

The last person to arrive is served first, and the first person waits longest. This is LIFO, so a stack models the service centre. Arrival is a push; serving a customer is a pop.

   arrive -> push                 serve -> pop
              | C3 | <- top  (served first)
              | C2 |
              | C1 | <- bottom (waits longest)

Algorithm

1. Create an empty stack S  (top = -1 for an array of size MAX)
2. Repeat until the simulation ends:
     if a customer c arrives:
         if S is full:  print "Centre full, customer turned away"
         else           PUSH(S, c)
     if the counter is free:
         if S is empty: print "No customer waiting"
         else           c = POP(S);  serve c
3. When closing time comes, customers left in S are never served (starvation).

PUSH(S, c):  if top == MAX-1 -> overflow;  else top = top + 1; S[top] = c
POP(S):      if top == -1    -> underflow; else c = S[top]; top = top - 1; return c

Example trace

If new customers keep arriving before the counter becomes free, C1 and C2 are never served, which is why the centre is "unfair".