1 list datastructures

Data Structures and Algorithms in Java 1/23
1. List Data Structure

Objectives
2
• Describe List structures
• Describe self-referential structures
• Explain types of linked lists
• Singly Linked Lists
• Circular Lists
• Doubly Linked Lists
• Lists in java.util

List Data Structures
• A list is a sequential data structure, i.e. it is a sequence of items of a given
base type, where items can be added, deleted, and retrieved from any
position in the list.
• A list can be implemented as an array, or as a dynamic array to avoid
imposing a maximum size.
• An alternative implementation is a linked list, where the items are stored
in nodes that are linked together with pointers. These two
implementations have very different characteristics.
• The possible values of this type are sequences of items of type BaseType
(including the sequence of length zero). The operations of the ADT are:
getFirst(), getLast(), getNext(p), getPrev(p), get(p),
set(p,x), insert(p,x), remove(p),removeFirst(),
removeLast(), removeNext(p), removePrev(p),
find(x),size()

Drawbacks of Arrays
4
• Array is a very useful data structure in many
situations. However, it has some important
limitations:
– They require size information for creation
– Inserting an element in the middle of an array leads to moving
other elements around
– Deleting an element from the middle of an array leads to moving
other elements around
• Other data structures are more efficient in such
situations.

Self-Referential Structures
Many dynamic data structures are implemented through the use of a self-
referential structure.
A self-referential structure is an object, one of whose elements is a
reference to another object of its own type.
With this arrangement, it is possible to create ‘chains’ of data of varying
forms:

11/12/2021 Data Structures and Algorithms in Java 6/23
DataNode
Employee info;
DataNode next;
trees
Linked lists
Employee
String name;
int age;
DataNode
Employee info;
DataNode left;
DataNode right;

Linked Lists
7
• A linked structure is a collection of nodes storing data
and links to other nodes
• A linked list is a linear data structure composed of nodes,
each node holding some information and a reference to
another node in the list
• Types of linked lists:
– Singly-Linked List
– Doubly-Linked List
In programming, linear means that they are described by one (single) series of data … ie.
Each data item has at most one predecessor and at most one successor.
And, Non-linear means anything else.
Linear are – Array, Linked List, Stack, Queue. Non Linear are – Tree, Graph

Singly Linked Lists
8
A singly linked list is a list whose node includes two
datafields: info and next. The info field is used to store
information, and this is important to the user. The next
field is used to link to its successor in this sequence
The following image depicts a simple integer linked list.
head tail
Singly Linked List

Singly Linked List Implementation
9
class Node
{int info;
Node next;
Node() {}
Node(int x, Node p)
{info=x;next=p;
}
}
void add(int x)
{ if(isEmpty())
head=tail=new Node(x,null);
else
{Node q =new Node(x,null);
tail.next=q; tail=q;
}
}
void traverse()
{Node p=head;
while(p!=null)
{System.out.print(" " + p.info);
p=p.next;
}
System.out.println();
}
Node search(int x) {...}
void dele(int x) {...}
}
class MyList
{Node head,tail;
MyList()
{head=tail=null;}
boolean isEmpty()
{return(head==null);
}
void clear()
{head=tail=null;
}

Singly Linked Lists - 1
10
Inserting a new node at the beginning of a list
Inserting a new node at the beginning of a Singly Linked List

11
Inserting a new node at the end of a list
Inserting a new node at the end of a Singly Linked List

Deleting a node from the beginning of a list
12
Deleting a node from the beginning of a Singly Linked List

Singly Linked List - 4
Deleting element from the end of a list
13
Deleting a node from the end of a Singly Linked List

Circular Lists - 1
14
• A circular list is when nodes form a ring: The
list is finite and each node has a successor
Circular SIngly Linked List

Circular Lists - 2
Inserting nodes
15
Inserting nodes at the front of a circular singly linked list (a) and at its end (b)

Circular List application
16
1. Round-Robin Scheduling
One of the most important roles of an operating system is in managing the
many processes that are currently active on a computer, including the
scheduling of those processes on one or more central processing units
(CPUs). In order to support the responsiveness of an arbitrary number of
concurrent processes, most operating systems allow processes to effectively
share use of the CPUs, using some form of an algorithm known as round-robin
scheduling. A process is given a short turn to execute, known as a time slice,
but it is interrupted when the slice ends, even if its job is not yet complete.
Each active process is given its own time slice, taking turns in a cyclic order.
2. Using circular linked list to implement Round-Robin Scheduling
We can use circular linked list to implement Round-Robin Scheduling by the
following method: rotate( ): Moves the first element to the end of the list.
With this new operation, round-robin scheduling can be efficiently
implemented by repeatedly performing the following steps on a circularly
linked list C:
1. Give a time slice to process C.first( )
2. C.rotate( )

Doubly Linked Lists - 1
17
• In a doubly linked list, each
node has two reference
fields, one to the successor
and one to the predecessor
class Node
{int info;
Node prev,next;
Node() {}
Node(int x, Node p, Node q)
{info=x;prev=p; next=q;
}
}
class MyList
{Node head,tail;
MyList() {head=tail=null;}
boolean isEmpty()
{return(head==null); }
void clear() {head=tail=null;}
void add(int x)
{if(isEmpty())
head=tail=new Node(x,null,null);
else
{Node q =new Node(x,tail,null);
tail.next=q;
tail=q;
}
}
...
}
Doubly Linked List

Doubly Linked Lists - 2
Adding a new node at the end
18
Adding new node at the end of Doubly Linked List

Doubly Linked Lists -3
Deleting a node from the end
19
Deleting a node from the end of Doubly Linked List

Lists in java.util - LinkedList class
boolean add(E o) Appends the specified element to the end of this list.
void addFirst(E o) Inserts the given element at the beginning of this list.
void addLast(E o) Appends the given element to the end of this list.
void clear() Removes all of the elements from this list.
E get(int index) Returns the element at the specified position in this list.
E getFirst() Returns the first element in this list.
E getLast() Returns the last element in this list.
E remove(int index) Removes the element at the specified position in
this list.
E removeFirst()Removes and returns the first element from this list.
E removeLast() Removes and returns the last element from this list.
int size() Returns the number of elements in this list.
Object[] toArray() Returns an array containing all of the elements in this list in the
correct order.

Lists in java.util
LinkedList class example
import java.util.*;
class Node
{ String name;
int age;
Node() {}
Node(String name1, int age1)
{ name=name1; age=age1;
}
void set(String name1, int age1)
{ name=name1; age=age1;
}
public String toString()
{ String s = name+" "+age;
return(s);
}
}
class Main
{
public static void main(String [] args)
{
LinkedList t = new LinkedList();
Node x; int n,i;
x = new Node("A01",25); t.add(x);
for(i=0;i<t.size();i++)
System.out.println(t.get(i));
}
}

Lists in java.util - ArrayList class
boolean add(E o) Appends the specified element to the end of this list.
void add(int index, E o) Inserts the given element at the specified pos.
void clear() Removes all of the elements from this list.
E get(int index) Returns the element at the specified position in this list.
E remove(int index) Removes the element at the specified position in this
list.
int size() Returns the number of elements in this list.
void ensureCapacity(int minCapacity) Increases the capacity of this ArrayList
instance, if necessary, to ensure that it can hold at least the number of elements
specified by the minimum capacity argument.
void trimToSize() Trims the capacity of this ArrayList instance to be the list's
current size.
Object[] toArray() Returns an array containing all of the elements in this list in the
correct order.

Summary
• A list is a sequential data structure, i.e. it is a
sequence of items of a given base type.
• A list can be implemented as an array, or as a dynamic
array to avoid imposing a maximum size.
• An alternative implementation is a linked list , where
the items are stored in nodes that are linked together
with pointers.
• A singly linked list is when a node has a link to its
successor (next node) only.
• A circular list is when nodes form a ring: The list is
finite and each node has a successor.
• A doubly linked list is when a node has links to its
previous and to the next nodes.

Reading at home
• 3 Fundamental Data Structures 103
• 3.1 Using Arrays - . 104
• 3.2 Singly Linked Lists - 122
• 3.3 Circularly Linked Lists - 128
• 3.4 Doubly Linked Lists - 132
Text book: Data Structures and Algorithms in Java

1 list datastructures

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