Question

Suppose that we start with an empty stack and execute the operations: push(5) push(12) popo) push(3) push(7) popo) What values are returned by the two pop() operations above, in order? First pop(): Second pop():

Answer 1

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push(5): 5 <--top
push(12): 5 12 <--top
pop(): 5 <--top  Value returned 12
push(3): 5 3<--top
push(7): 5 3 7<--top
pop(): 5 3<--top Value returned 7

f = front, r = rear
enqueue(5):
5
f,r
enqueue(12):
5 12
f  r
dequeue()
12    value returned from front 5
f,r
enqueue(3):
12 3
f  r
enqueue(7):
12 3 7
f    r
dequeue():
3 7    value returned 12
f r 

First Pop(): 12

First Pop(): 7

First Deque: 5

Second Deque: 12