introduction to stacks & queues

1. STACKS & QUEUES

2. STACKS
AA ssttaacckk iiss aa rreessttrriicctteedd lliinneeaarr lliisstt iinn wwhhiicchh aallll aaddddiittiioonnss
aanndd ddeelleettiioonnss aarree mmaaddee aatt oonnee eenndd,, tthhee ttoopp.. IIff wwee iinnsseerrtt aa
sseerriieess ooff ddaattaa iitteemmss iinnttoo aa ssttaacckk aanndd tthheenn rreemmoovvee tthheemm,,
tthhee oorrddeerr ooff tthhee ddaattaa iiss rreevveerrsseedd.. TThhiiss rreevveerrssiinngg aattttrriibbuuttee
iiss wwhhyy ssttaacckkss aarree kknnoowwnn aass llaasstt iinn,, ffiirrsstt oouutt ((LLIIFFOO)) ddaattaa
ssttrruuccttuurreess..
Figure:-Three representations of stacks

3. Operations on stacks
There are four basic operations, stack, push, pop and empty,
that we define in this chapter.
The stack operation
The stack operation creates an empty stack. The following
shows the format.
Figure:- Stack operation

4. The push operation
The push operation inserts an item at the top of the stack.
The following shows the format.
Figure:- Push operation

5. The pop operation
The pop operation deletes the item at the top of the stack.
The following shows the format.
Figure:- Pop operation

6. The empty operation
The empty operation checks the status of the stack. The
following shows the format.
This operation returns true if the stack is empty and false if
the stack is not empty.

7. Stack ADT
We define a stack as an ADT as shown below:

8. Example 1
Figure 1 shows a segment of an algorithm tthhaatt aapppplliieess tthhee
pprreevviioouussllyy ddeeffiinneedd ooppeerraattiioonnss oonn aa ssttaacckk SS..
Figure 1:- Example 1

9. Figure:- Stack implementations

10. QUEUES
AA qquueeuuee iiss aa lliinneeaarr lliisstt iinn wwhhiicchh ddaattaa ccaann oonnllyy bbee
iinnsseerrtteedd aatt oonnee eenndd,, ccaalllleedd tthhee rreeaarr,, aanndd ddeelleetteedd ffrroomm tthhee
ootthheerr eenndd,, ccaalllleedd tthhee ffrroonntt.. TThheessee rreessttrriiccttiioonnss eennssuurree tthhaatt
tthhee ddaattaa iiss pprroocceesssseedd tthhrroouugghh tthhee qquueeuuee iinn tthhee oorrddeerr iinn
wwhhiicchh iitt iiss rreecceeiivveedd.. IInn ootthheerr wwoorrddss,, aa qquueeuuee iiss aa ffiirrsstt
iinn,, ffiirrsstt oouutt ((FFIIFFOO)) ssttrruuccttuurree..
Figure:- Two representation of queues

11. Operations on queues
Although we can define many operations for a queue, four
are basic: queue, enqueue, dequeue and empty, as defined
below.
The queue operation
The queue operation creates an empty queue. The following
shows the format.
Figure:- The queue operation

12. The enqueue operation
The enqueue operation inserts an item at the rear of the
queue. The following shows the format.
Figure:- The enqueue operation

13. The dequeue operation
The dequeue operation deletes the item at the front of the
queue. The following shows the format.
Figure:- The dequeue operation

14. The empty operation
The empty operation checks the status of the queue. The
following shows the format.
This operation returns true if the queue is empty and false if
the queue is not empty.

15. Queue ADT
We define a queue as an ADT as shown below:

16. Example 2
Figure 2 shows a segment of an algorithm tthhaatt aapppplliieess tthhee
pprreevviioouussllyy ddeeffiinneedd ooppeerraattiioonnss oonn aa qquueeuuee QQ..
Figure 2:- Example 2

17. Figure:- Queue implementations

18. THANK YOU