linklisr
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Linked Lists An Alternative Collections Data Structure What Is A Linked List? A data structure using memory that expands and shrinks as needed Relies on identical nodes “pointing” or “linked” to other nodes Each node is an instance of a class (i.e. an object) Head Example Declarations public class IntNode { private int data; private IntNode link; … } OR public class Part { private int partNo; private double price; private Part link; … }
Transcript of linklisr
Linked Lists
An Alternative Collections Data Structure
What Is A Linked List?
A data structure using memory that expands and shrinks as neededRelies on identical nodes “pointing” or “linked” to other nodesEach node is an instance of a class (i.e. an object)
Head
Example Declarations
public class IntNode{
private int data;private IntNode link;…
}OR
public class Part{
private int partNo;private double price;private Part link;…
}
Special Nodes
Head nodeThe first node in a linked listAlmost all programs using linked lists will maintain a pointer to the head nodeAn empty list is represented by storing Null in the head variable
Tail nodeThe last node in a linked listMany programs maintain a pointer to the tail nodeA tail node points to a “null” referenceIn an empty list tail will also be Null
Necessary Methods
Methods to access and modify data:e.g. getData(), getLink(), setData(int
newData), setLink(??? newLink)Methods for creating nodesi.e. constructors
Methods for adding and removing nodes
Caution!
Always make sure that your linked list methods work correctly with an empty list.
Adding a Node to the Front of a List1. Create a new node with the desired data, and
the link pointing to the current head node2. Make the “head” pointer point to the new nodeWhat happens if we started with an empty list?
Head
remove
Removing the First Node of a List
Make the head pointer point to what the current head node is pointing to
What happens to the original head node?What if there was only one node in the list?
Head
remove
Adding a Node After a Selected Node
1. Create a new node pointing to whatever the selected node is currently pointing to
2. Make the selected node point to the new nodeWhat happens if the selected node was the last node
in the list?
Head
remove
Selected
Removing a Selected Node
Head
SelectedCan we remove this?
Removing the Node After a Selected Node
HeadSelected Can we remove this?
HeadSelected
Desired Result:
What happens if we removed the tail node?
Manipulating Entire Linked Lists
Traverse the entire list in a loop that terminates when the null pointer is reachedIn the body of the loop perform the necessary operation(s)
Manipulating Entire Linked Lists
Examples: count the elements of the listPrint the elements of the listUpdate the values in the list (e.g. increase all prices by 10%)
If implemented in the same class as the node (i.e. no separate list class), it is better to use static methods, this way the method can be used for empty lists
Sample Code
IntNode current;for (current = head; current != null; current = current.link){
…}
Or:IntNode current;current = head;while (current != null){
…current = current.link;
}
Copying an Entire List
public static IntNode copyList (IntNode head){
if (head == null) return null;IntNode copyHead = new IntNode (head.data,null);IntNode copyTail = copyHead;IntNode source = head;while (source.link != null){
source = source.link;copyTail.addNodeAfter(source.data);copyTail = copyTail.link;
}return copyHead;
}
Copying a Part of a List
Given a start node and an end node make a copy of that part of the listCan we return both the head and tail of the copy?How does the method work? Is it that much different from copying the full list?
Linked List Application –IntLinkedBag
Keeps track of integer elementsCan add or delete elementsAnswers questions about its elementsCan add all the contents of another bagGrows and shrinks in size as needed
IntLinkedBag - Methods
public void add (int element)public void addAll (IntLinkedBag addend)public int countOccurences(int target)public boolean remove (int target)public int size()public void trimToSize()public static IntLinkedBag union (IntLinkedBag b1,
IntLinkedBag b2)public int grab()public void ensureCapacity (int minimumCapacity) ???public int getCapacity() ???
Another Linked List Application - DoubleLinkedSeq
Similar to bag but sequence is preservedAn additional instance variable is needed to hold the position of the “current” elementTwo additional instance variables “tail” and “precursor” may be used for convenienceSome methods can be preserved, others must be modifiedAdditional methods are neededImplementation: assignment 5
Doubly Linked Lists
Similar to linked lists with pointers in both directions
Head Tail
Array vs. Linked Lists vs. Doubly Linked Lists
Which is better for the following operations?:
Random accessFrequent additions/removals in the middle of a sequenceFrequent forward and backward searching of a sequenceFrequent size changes
