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AMay 2004 B C D E F G H I J K L M

N O P Q R S O T U V R T R P W X W O Y P Z

[Structure built from collection of nodes that reference each other. [A node \

contains reference to a list element, \one or more variables referencing other structure nodes.

]May 2004 B C D E F G H I J K L M

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[LinkedList: Each node references node containing next list element.

node

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[Class Node, local to LinkedList, models nodes. [Node structure: \

must know an element of the List, \must know the next Node in sequence. [

As local class of LinkedList has no methods.

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public class LinkedList<Element> extends AbstractList<Element> {

…private class Node {

private Element element;private Node next;

// Create a Node containing the specified element.public Node (Element element) {

this.element = element;this.next = null;

}} // end of class Node

} // end of class LinkedList

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public class LinkedList<Element> extends AbstractList<Element> {

private int size;private Node first;

// Create an empty LinkedList<Element>.public LinkedList () {

size = 0;first = null;

}…

}

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/*** The i-th node of this LinkedList.* The LinkedList must be non-empty.* require 0 <= i && i < this.size()*/

private Node getNode (int i) {Node p = first;int pos = 0; // p is pos-th Nodewhile (pos != i) {

p = p.next;pos = pos + 1;

}return p;

}

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public Element get (int index) {Node p = getNode(index);return p.element;

}

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Given an index referencing a node to be removed::

Find previous node referencing it.:Update that node’s next;

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ARecall getNode requires argument to be greater than or equal to 0. AIf index is 0, it’s not legal to writeNode p = getNode(index-1);

ASpecial case: index 0 removes first linked list elementB

instance variable first of the LinkedList object must be modified.

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public void remove (int index) {if (index == 0)

first = first.next;else {

Node p = getNode(index-1);p.next = p.next.next;

}size = size - 1;

}

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Node newNode = new Node(element);

if (index == 0) {newNode.next = first;

first = newNode;

} else {Node p = getNode(index-1);

newNode.next = p.next;p.next = newNode;

}size = size + 1;®

}

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public void remove (int index) {

if (size == 1) { // remove only elementfirst = null;

last = null;}else if (index == 0) {//remove first element

first = first.next;

}else {Node p = getNode(index-1);

p.next = p.next.next;if (index == size-1) //last element removed

last = p;}

size = size - 1;

}

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-“dummy” node .

Always present at front of list,.

contains no element, .first always references header node,

.first is never null.

-Reduces special cases in the implementation of some methods.

/ 0May 2004 1 2 3 4 5 6 7 8 9 : ; <

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�Assuming Header extends Node DoublyLinkedListconstructor creates header Node, and links it to itself.

public DoublyLinkedList () {

size = 0;

header = new Header();

header.next = header;

header.previous = header;

}

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�Element access by index is linear. �Would not use a linked implementation if primary operation is to access randomly by index.�Method get uses getNode: requires i steps to get Node with index i.

� �May 2004 � � � � � � � � �

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�indexOf uses method get.�If element not found, get executes n times, with index values 0 through n-1:

value of i: 0 1 2 … n-1

steps of get(i): 0 1 2 … n-1�Steps require: 0 + 1 + 2 + … + (n-1) = (n2-n)/2.�Method is quadratic.

' (May 2004 � � � � � � � � �

) * + , - . / * - * 0 1 2 1 , 3 0 3 4 , 0 5 * 6 7 4

public int indexOf (Element element) {Node p = first;

int pos = 0;while (p != null && !element.equals(p.element)) {

p = p.next;pos = pos+1;

}

if (p == null)return -1;

elsereturn pos;

}8Method is linear.8But uses private members of the classLinkedList.