cop 3503 fall 2012 shayan javed lecture 18

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COP 3503 FALL 2012SHAYAN JAVED

LECTURE 18

Programming Fundamentals using Java

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Data Structures

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So far...

Looked at Arrays and ArrayLists as our data structures

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So far...


Very useful, but not always the best options

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So far...


Very useful, but not always the best options

Going to look at some other data structures

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Data Structures

Stack Queue Linked List Trees Graph Hashtable etc.

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Data Structures

Stack Queue Linked List Trees Graph Hashtable etc.

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Stack

Last-In-First-Out (LIFO) Data Structure

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Stack


Basically...a stack of data.

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Stack



Used when you want the oldest added data first.

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Stack




Abstract data type (can store any kind of data).

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Stack

Three Operations:

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Stack

Three Operations:

push(Object): Pushes an object on top of a stack

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Stack

Three Operations:


pop(): Returns the object at the top of the stack and removes it

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Stack

Three Operations:


pop(): Returns the object at the top of the stack and removes it

peek(): Returns the object at the top without removing it

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Stack

Some uses:

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Stack

Some uses:

“Stack Frame” for method calls.

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Stack

Some uses:

“Stack Frame” for method calls.

Used for evaluating arithmetic expressions: (prefix, postfix, infix)

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Stack

Java provides a Stack class (java.util.Stack)

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Stack


Has all the operations

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Stack



But how does it actually store the data? (What’s the “back-end”?)

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Stack



But how does it actually store the data? (What’s the “back-end”?)

Uses the java.util.Vector class (similar to ArrayList)

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Queue

A First-In-First-Out (FIFO) data structure.

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Queue



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Queue



Often used for scheduling (handle first in line)

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Queue

Three Operations:

enqueue(Object): Adds an object to the queue

dequeue(): Returns the object at the front of the queue and removes it

peek(): Returns the object at the front without removing it

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Queue

Java provides a Queue interface (java.util.Queue)

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Queue


Has all the operations enqueue = add dequeue = poll

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Queue



Interface implemented in classes like LinkedList

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Queue



Interface implemented in classes like LinkedList

Queue<Integer> queue = new LinkedList<Integer>();

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Arrays and ArrayLists

Work well in a lot of cases.

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Can use as “back-end” data structures

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But where do they fall short?

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But where do they fall short? Data retrieval – excellent O(1)

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But where do they fall short? Data retrieval – excellent O(1) Adding data

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But where do they fall short? Data retrieval – excellent O(1) Adding data – inefficient O(n) in some cases

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But where do they fall short? Data retrieval – excellent O(1) Adding data – inefficient O(n) in some cases

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But where do they fall short? Data retrieval – excellent O(1) Adding data – inefficient O(n) in some cases Fixed size – have to shift/copy to new array

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What if your application requires a lot of adds but not retrievals?

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What if your application requires a lot of adds but not retrievals?

Use Linked Lists

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Linked List

A list – a collection of linked nodes.

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Linked List


Dynamic data structure – size is not fixed, and memory is not contiguous (unlike an array)

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Linked List



Insertion to the list is very fast – O(1) in most cases

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Linked List



Insertion to the list is very fast – O(1) in most cases

Indexing is slow. Random access also not possible

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Linked List

Many variations:

Singly-Linked List (can only traverse forward) Doubly-Linked List (can traverse in reverse too) Circular Linked Lists Multi-Linked Lists etc.

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Node

Basic structure – collection of linked nodes make a linked list.

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Node


Stores some data and a link to the next Node.

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Node



int null

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Node



int int null

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Singly-Linked List (SLL)

Nodes connected to each other

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int int nullint

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SLL only stores links to two nodes:

int int nullint

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SLL only stores links to two nodes: Head node (front)

int int nullint

head

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SLL only stores links to two nodes: Head node (front) Tail node (end)

int int nullint

head tail

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Operations: LinkedList(): create an empty list

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Operations: LinkedList(): create an empty list append(Object): add to the end

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Operations: LinkedList(): create an empty list append(Object): add to the end insert(Object, index): add at a certain index

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Operations: LinkedList(): create an empty list append(Object): add to the end insert(Object, index): add at a certain index remove(index): remove Object at index remove(Object): remove Object

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Operations: LinkedList(): create an empty list append(Object): add to the end insert(Object, index): add at a certain index remove(index): remove Object at index remove(Object): remove Object get(Object): return index of Object get(index): return Object at index

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Operations: LinkedList(): create an empty list append(Object): add to the end insert(Object, index): add at a certain index remove(index): remove Object at index remove(Object): remove Object get(Object): return index of Object get(index): return Object at index size(): return size of the list

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Operations: LinkedList(): create an empty list append(Object): add to the end insert(Object, index): add at a certain index remove(index): remove Object at index remove(Object): remove Object get(Object): return index of Object get(index): return Object at index size(): return size of the list clear(): empty the list

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Create an Empty SLL:

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head tail

null

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public SLL() {

head = null;

tail = null;

}

head tail

null

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append(Object):

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append(Object):

Create a Node with that Object

Obj null

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append(Object):


Obj null

head tail

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append(Object): append another object

Obj null

head tail

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Obj null

head tail

Obj null

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Create a Node with that Object Make tail point to it

Obj

head tail

Obj null

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Create a Node with that Object Make tail point to it Update tail Node

Obj

head tail

Obj null

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size():

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size():

Obj

head tail

Obj nullObj Obj

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size():

Obj

head tail

Obj nullObj Obj

temp

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size():

Obj

head tail

Obj nullObj Obj

temp

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size():

Obj

head tail

Obj nullObj Obj

temp

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size():

Obj

head tail

Obj nullObj Obj

temp

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size():

Obj

head tail

Obj nullObj Obj

temp

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size():

Keep incrementing until you reach “null”.

Obj

head tail

Obj nullObj Obj

temp

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get(Object): Returns index of first Node with that object

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You should know how to traverse

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Compare object with equals() method

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Compare object with equals() method Return index if found -1 if not found

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remove(Object):

Obj

head tail

Obj nullObj Obj

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remove(Object):

Obj

head tail

Obj nullObj Obj

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remove(Object):

Obj

head tail

Obj nullObj Obj

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remove(Object):

Obj

head tail

Obj nullObj

Obj

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remove(Object):

Obj

head tail

Obj nullObj

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remove(Object):

remove(index) - remove at a certain index remove(Node) - remove a certain Node

Work the same way

Obj

head tail

Obj nullObj

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So now we know how to: append, prepend, insert

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So now we know how to: append, prepend, insert find the size

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So now we know how to: append, prepend, insert find the size find the index of a specific element

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So now we know how to: append, prepend, insert find the size find the index of a specific element remove an object/Node

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So now we know how to: append, prepend, insert find the size find the index of a specific element remove an object/Node

What about sorting?

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Sorting:

Bubble Sort Selection Sort Insertion Sort

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Sorting:

Bubble Sort Selection Sort Insertion Sort

How many of these can you implement for Linked Lists?

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Sorting: We should swap nodes

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Obj

head tail

Obj nullObj Obj

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Obj

head tail

Obj nullObj Obj

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Obj

head tail

Obj null

Obj

Obj

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Obj

head tail

Obj null

Obj

Obj

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Obj

head tail

Obj null

Obj

Obj

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Obj

head tail

Obj nullObjObj

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How many nodes were changed?

Obj

head tail

Obj nullObjObj

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How many nodes were changed? 3

Obj

head tail

Obj nullObjObj

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Swap:

Obj

head tail

Obj nullObj Obj Obj

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Swap:

Obj

head tail

Obj nullObj Obj Obj

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Swap:

Also have to modify the ones before them

Obj

head tail

Obj nullObj Obj Obj

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Swap:


Obj

head tail

Obj nullObj Obj Obj

node1 node2

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Swap:


Obj

head tail

Obj nullObj Obj Obj

node1 node2

node1P node2P

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Swap: RESULT:

Also have to modify the ones before them We have now seen two cases

Obj

head tail

Obj nullObj Obj Obj

node2 node1

node1P node2P

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Singly-Linked List (SLL)void swap(Node node1, Node node2, Node node1P, Node node2P) {

if (node1.next == node2) { // side-by-side (1st case)

node1.next = node2.next;

node2.next = node1;

}

else { // 2nd case

Node temp = node1.next;


node2.next = temp;

node2P.next = node1;

}

if (node1P != null) // why?


// what about the head and tail nodes?

// update them accordingly

}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;

node2P.next = node1; // the node before node2

}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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node2.next = node1;

}

else { // 2nd case



node2.next = temp;


}





}

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Sorting: So swap is not straightforward

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Once you figure out swap, you can implement Bubble and Selection Sort

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Once you figure out swap, you can implement Bubble and Selection Sort

Try to implement the Sorting Methods for Linked Lists

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Summary

Arrays/ArrayLists: useful data structures but not always optimal. Retrieval very quick, insertion can be slow

Stacks/Queues: Abstract data types useful for LIFO/FIFO storage. Implemented using arrays/SLLs

Linked Lists: Alternative to arrays – insertion is fast but retrieval is slow.

cop 3503 fall 2012 shayan javed lecture 18

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