queue adt operations enqueue, dequeue, peek, isempty implementation: circular array (weiss), linked...

Queue ADTOperations• Enqueue, Dequeue, Peek, isEmpty

Implementation: • Circular Array (Weiss),• Linked List,• Circular Array (text)

Application:

Level-Order Tree Traversal

Implementing a Queue

• Using Vector /Array – requires estimate of maximum queue length– may grow dynamically– Ø = empty slots– Can contain varied data/objects (not necessarily

homogeneous)

28-17 Golf #1 Ø Ø Ø212 rules!

rearfront


• Using Linked List– flexible, adjusts to problem size– implementing a linked list

• nodes and references/links/pointers

front 212 rules!28-17 Ø

rear

Golf #1


• Using Linked List– implementing a linked list

• cursor implementation

front = 5

freelist = 8

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Golf #1

212 rules!

28-17

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rear = 1


Vector/Array Linked List

– enqueue O(1)* O(1)– dequeue O(1) O(1)– peek O(1) O(1)– isEmpty O(1) O(1)

*assuming no need for Vector/Array expansion

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enqueue (Object item) { rear = (rear+1)%Q.length; if (front == rear) throw QueueFullException; Q[rear] = item;} // enqueue

Object dequeue() { if (front == rear) throw QueueEmptyException; front = (front+1)%Q.length; return Q[front];} // dequeue

front = 0

rear = 0

Q

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front = 0

rear = 0 1enqueue (“A”)

A

Q

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front = 0

rear = 1 2enqueue (“B”)

A

B

Q

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front = 0

rear = 2 3enqueue (“C”)

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B

C

Q

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front = 0 1

rear = 3dequeue()

// returns “A”

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C

Q

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front = 1 2

rear = 3dequeue()

// returns “B”

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B

C

Q

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front = 2 3

rear = 3dequeue()

// returns “C”

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C

Q

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boolean isEmpty() { } // isEmpty front = 3

rear = 3// Is the queue empty?// Complete isEmpty() method.

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Q

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boolean isEmpty() { return (front == rear); } // isEmpty front = 3

rear = 3 4enqueue(“D”);

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C

Q

D

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rear = 4 5enqueue(“E”);

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Q

DE

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rear = 5 6enqueue(“F”);

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Q

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DE

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rear = 6 7enqueue(“G”);

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Q

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G

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rear = 7 0enqueue(“H”);

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rear = 0 1enqueue(“I”);

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rear = 1 2enqueue(“J”);

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front = 3

rear = 2

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boolean isEmpty() { return (front == rear); } // isEmpty

boolean isFull() { } // isFull

// Is the queue full?// Complete isFull() method.

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front = 3 4

rear = 2

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boolean isFull() { return front==(rear+1)%Q.length;} // isFull

dequeue();// returns “D”

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front = 4 5

rear = 2

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dequeue();// returns “E”

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front = 5

rear = 2

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// How many elements does the// queue have? Generalize.

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Level-Order Traversal

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I J K

M NL

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Level-Order Traversal

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M NL

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Level 0

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levelOrder (Node root) { Queue q; q.enqueue (root); while (!q.isEmpty()) { Node n = (Node) q.dequeue(); visit(n); if (n.left() != null) q.enqueue(n.left()); if (n.right() != null) q.enqueue(n.right()); } // while} // levelOrder

q = Ø

output =

B

D

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I J K

M NL

F

H

C

G


q A

output =

B

D

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I J K

M NL

F

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q B C

output = A

B

D

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I J K

M NL

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q C D E

output = A B

B

D

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I J K

M NL

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C

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q D E F G

output = A B C

etc.

queue adt operations enqueue, dequeue, peek, isempty implementation: circular array (weiss), linked...

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