Tutorial 5Linked List Variations, Stack, & Queue

Linked List Variations (1)

• Two weeks ago, we have reviewed “Single Linked List”– Revisited in Stack data structure later

• There exists several Linked List Variations:– With or without Tail Pointer?

– One link or double links per node?

– Circular or not?

– And combinations of these…

• Next slides: some diagrams of the variations asked in Q1, then one of you will explain the differences (max hops, memory space)!

Node 1 Node 2

Node ...

Node N

Head

Linked List Variations (2)

• Single Linked List with Tail Pointer– Other than head, we also have tail pointer pointing to the last item

– Pro: Can visit the tail very fast or add new item from tail – Cons: Slow to delete the tail… – Revisited in Queue data structure later

Node 1 Node 2

Node ...

Node N

Head Tail

Linked List Variations (3)

• Circular Single Linked List– Tail.Next = Head at tail, the link cycles back to the head

– Pro: Can visit all node from any node , good for Round Robin stuffs

– Cons: Slow to delete the tail… – Can choose to remember Tail only, save one pointer…

Node 1 Node 2

Node ...

Node N

Head

Node 1 Node 2

Node ...

Node N

Tail

Linked List Variations (4)

• Double Linked List– Two pointers per node: forward/backward

– Pro: Can go backwards

– Pro: If you have tail pointer, you can also delete tail efficiently! – Cons: Extra pointer is an overhead… – Can be circular or not…, with or without tail…

Node 1 Node 2

Node ...

Node N

Head

Node 1 Node 2

Node ...

Node N

Head

Linked List Variations (5)

• Single Linked List with dummy head node– Pro: Simplify Single Linked List code

– Cons: Same as standard Single Linked List

• We will discuss their pro/cons in Q1 • Be careful, the lecturers can vary these combinations and

ask you something about such variations in the mid/final exam…– Make sure you understand these concepts!

Dummy Node 1

Node ...

Node N

Head

• Behavior: Last In First Out (LIFO)• Stack implemented using Array with top pointer

– http://www2.latech.edu/~box/ds/Stack/Stack.html

• (Perhaps) the best implementation?– Using Single Link List with head pointer only– http://www.cosc.canterbury.ac.nz/people/mukundan/dsal/LinkListAppl.html

Stack

Node 1 Node 2

Node ...

Node N

Head

ADT Stack using SLL as underlying data structure

Node 1

Node 2

Node ...

Node N

Head isTop of Stack

Node 0 Top: efficientPush: efficientPop: efficient

• Behavior: First In First Out (FIFO)• Queue implemented using Circular Array

– http://maven.smith.edu/~streinu/Teaching/Courses/112/Applets/Queue/myApplet.html

• Better: use Single Linked List with Tail Pointer– Head pointer for dequeue/front, Tail pointer for enqueue/back

• We set these roles because pointer directions in SLL (arrows to the right) imply that only insertion is efficient at tail (thus only ok for enqueue) and both insertion/deletion are efficient at head (but since we already use tail for enqueue, head is for dequeue)

– Or use Circular Single Linked List: save 1 pointer: Head = Tail.next

ADT Queue using SLL with tail pointer as underlying data structure, circular SLL also ok

Queue

Node 1 Node 2

Node ...

Node N

HeadFront of Queue

Tail =Rear of Queue

Node N+1

Back: efficientEnqueue: efficient

Front: efficientDequeue: efficient

Student Presentation

• T5:1. ><

2. Ramanathan Anu

3. ><

4. Sal Visoth

• T10:1. Puranik Pranay

2. Sistla

3. Suresh

4. ><

• T13:1. Mai Xiangjun

2. Nikhil

3. Oh Kok Wei

4. Peck Shan Ren

• T9:1. ><

2. Nguyen Sy Nguyen

3. Sandhya

4. ><

• T17:1. Kalpit Jain

2. ><

3. Lee Jia Yi

4. Lee Yue Ting

9

Follow Up Questions

• Q1– What other “creative” linked lists that you can think of?

• Q2:– Using stack to do this is a bit overkill…– Can you help Mr Scramble WITHOUT using stack?

• It is actually much easier

• Q3:– Again, using stack to do this is also overkill– Can you do this WITHOUT using stack?

• It is actually much easier

• Q4:– What if you reverse all the links? (reversed single linked list)

• With head pointer only?

• With both head and tail pointers?

10

Midterm Test Tips

• Analyzing the topics:– C/C++: Likely used as part of question in the essay

• But may appear as standalone question in MCQ

– ADT: Likely embedded in Linked List/Stack/Queue question in essay

– List ADT: Vector versus Linked List idea, we spend two weeks here, most likely this appear as the essay?

• If you want to put a bet, this is your best bet…

– Stack and Queue: likely appear but perhaps? less emphasisas this just recently taught…

• Try:– Mixing and matching various data structure implementations:

• Funny variants of linked list• Implementing stacks or queues using funny data structures, etc…

– Try implementing queue using “circular vector”, it is tricky