StackandQueue

6/19/16 1

CMSC132,Summer2016Object-OrientedProgrammingII

AnwarMamat

Stack

• Allowsaccesstoonlythelastiteminserted.

• Anitemisinsertedorremovedfromthestackfromoneendcalledthe“top” ofthestack.

• ThismechanismiscalledLast-In-First-Out(LIFO).

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StackExample

• EmptyStack

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StackExample

• Stack

Push10

10Top

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StackExample

• Stack

Push10

10

Top

Push20

20

Push30

30

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StackExample

• Stack

Push10

10Top

Push20

20

Push30

Pop

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StackExample

• Stack

Push10

10

Top

Push20

20

Push30

PopPush10

10

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Applications

• JVMstackmachine• FunctionCall• ExpressionEvaluation• PushdownAutomata• Recursiveà IterativeFunctionConversion

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StackInterface

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ImplementStackUsinganArray

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StackExample

• EmptyStack

N

4

3

2

1

0

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Pushinganitem

N

4

3

2

1

0

Push10

10

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Pushingmoreitems

N

4

3

2

1

0 10

Push10

Push20

Push30

20

30

Whatifthearrayisfull?

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Removinganitem

N

4

3

2

1

0 10

Push10

Push20

Push30

20Pop

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Removinganitem

N

4

3

2

1

0 10

Push10

Push20

Push30

20Pop

Pop

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ArrayImplementation:push

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N

4

3

2

1

0 10

ArrayImplementation:pop

Why?

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ArrayImplementation:peek

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ImplementStackUsingaLinkedList

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StackExample

• EmptyStack

first=nullN=0

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Pushinganitem

firstN=1

10

Push10

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Pushingmoreitems

firstN=3

30

Push10

Push20

Push30

1020

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Pushingmoreitems

firstN=2

20

Push10

Push20

Push30

10

Pop

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OthermethodsPeek

size

isEmpty

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TestingtheStack

Size:77,7,6,6,5,5,4,4,3,3,2,2,1,16/19/16 25

Queue• QueueisanADTdatastructuresimilartostack,exceptthatthefirstitemtobeinsertedisthefirstonetoberemoved.

• ThismechanismiscalledFirst-In-First-Out(FIFO).• Placinganiteminaqueueiscalled“insertionorenqueue”,whichisdoneattheendofthequeuecalled“rear”.

• Removinganitemfromaqueueiscalled“deletionordequeue”,whichisdoneattheotherendofthequeuecalled“front”.

• Applications:printerqueue,keystrokequeue,etc.

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Queue

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QueueExampleEmptyQueue

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AddinganitemEmptyQueue

enqueue 10

10

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AddingmoreitemsEmptyQueue

enqueue 10

30

enqueue 20

20

enqueue 30

10

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AddingmoreitemsEmptyQueue

enqueue 10

30

enqueue 20

20

enqueue 30dequeue

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QueueInterface

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CircularArrayImplementation

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012345

first last

N=0

CircularArrayImplementation

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10 20 30

012345

first last

enqueue 10

enqueue 20enqueue 30

N=3

CircularArrayImplementation

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20 30

012345

first last

enqueue 10

enqueue 20enqueue 30

dequeueN=2

CircularArrayImplementation

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20 30 40 50

012345

first last

enqueue 10

enqueue 20enqueue 30

dequeueN=4

enqueue 40enqueue 50

CircularArrayImplementation

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20 30 40 50 60

012345

firstlast

enqueue 10

enqueue 20enqueue 30

dequeueN=5

enqueue 40enqueue 50enqueue 60

CircularArrayImplementation

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30 40 50 60

012345

firstlast

enqueue 10

enqueue 20enqueue 30

dequeueN=4

enqueue 40enqueue 50enqueue 60dequeue

Implementingpush(enqueue)

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30 40 50 60

012345

firstlast

Implementingpop(dequeue)

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30 40 50 60

012345

firstlast

Implementingresize

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70 30 40 50 60

012345

firstlast

30 40 50 60 70

first last

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ImplementQueueUsingaLinkedList

firstN=3

10 3020

last

• Addanewitem• Newnodeisadded totail(last.next)

• Removeaitem• Removethefirstnode (first=first.next)