1. Lists, Queues,
Stacks
CST200 – Week 5: Array based Implementation
Instructor: Andreea Molnar

2. Outline
• Lists
• Queues
• Stacks

3. List
A sequence of items that has at least the
functionality below:
• Accessing an item at a given position
• Adding an item at a given position
• Removing an item
• Determining the number of items

4. Stack
A sequence of items in which:
•
•
An item can be inserted only to the top
Only the top item can be
accessed/removed
In a stack items are inserted and removed
according to the last-in first-out (LIFO)
principle.

5. Stack
Functionality:
•
•
•
•
•
push: insert an item to the top of the stack
pop: remove the item at the top of the stack
peek: get the item at the top of the stack
isEmpty: assess if the stack is empty
isFull: assess if the stack is full

6. Stack
Assuming that one has an object myStack:
myStack.push (25)
25
mySta
ck

7. Stack
Assuming that one has an object myStack:
myStack.push (25)
myStack.push (10)
10
25
mySta
ck

8. Stack
Assuming that one has an object myStack:
myStack.push (25)
myStack.push (10)
10
25
mySta
ck
int topValue = myStack.pop ()
10
topVa
lue

9. Stack
Assuming that one has an object myStack:
myStack.push (25)
myStack.push (10)
int topValue = myStack.pop ()
5
25
mySta
ck
myStack.push (5)
10
topVa
lue

10. Stack
Assuming that one has an object myStack
myStack.push (25)
myStack.push (10)
5
25
mySta
ck
int topValue = myStack.pop ()
myStack.push (5)
10
topVa
lue

11. Stack
Assuming that one has an object myStack:
myStack.push (25)
myStack.push (10)
int topValue = myStack.pop ()
myStack.push (5)
myStack.push (20)
20
5
25
10
mySta
ck
topVa
lue

12. Stack
Assuming that one has an object myStack:
myStack.push (25)
myStack.push (10)
int topValue = myStack.pop ()
myStack.push (5)
myStack.push (20)
topValue = myStack.pop ()
20
5
25
20
mySta
ck
topVa
lue

13. Queue
A sequence of items in which the first
element inserted is the first one to be
removed.
In a queue elements are inserted and
removed based on the the first-in first-out
(FIFO) principle.

14. Queue
Functionality:
•
•
•
enqueue: add an item to the back of the queue
dequeue: remove the front item
getFront: get the front item

15. Queue
Assuming that one has an object myQueue:
myQueue.enque (25)
25
myQue
ue

16. Queue
Assuming that one has an object myQueue:
myQueue.enque (25)
int value = myQueue.deque ()
25
25
myQue
ue
value

17. Queue
Assuming that one has an object myQueue:
myQueue.enque (25)
int value = myQueue.deque ()
20
myQueue.enque (20)
25
myQue
ue
value

18. Queue
Assuming that one has an object myQueue:
myQueue.enque (25)
int value = myQueue.deque ()
myQueue.enque (20)
20
5
myQue
ue
myQueue.enque (5)
25
value

19. Queue
Assuming that one has an object myQueue:
myQueue.enque (25)
int value = myQueue.deque ()
myQueue.enque (20)
20
5
myQueue.enque (5)
value = myQueue.deque ()
20
myQue
ue
value

20. Summary
•
•
•
A list is sequence of items that allows to access, add
and remove an arbitrary element and determine the
numbers of items (length/size of the list).
A stack is a data structure in which an item can be
added, accessed or removed only from the top.
A queue is a data structure in which the first element
added is the first one to be accessed/removed.