Embed Size (px)
Citation preview
1
Java linked list
Java linked list - definition▪ Often in programming we are required to systematically store some type of
information. A prime example of this is to use arrays, but when you don’t know
the amount of information to be stored we need a dynamic data structure.
▪ One option for us is to use a linked list. A linked list works by creating a
collection of objects (nodes) which both carry the data we want to store and a
reference to the next node in the list.
▪ There is more than one type of a linked list. Some different type of
linked list are shown below:
1. Singly linked list.
Root node links one way through all the nodes.
Last node links to NULL.
2. Doubly linked list.
Every nodes stores a reference to its previous node as well as its
next. Last node links to NULL.
2
Java linked list, cont.3. Circular linked list.
Circular linked list have a reference to one node which is the tail
node and all the nodes are linked together in one direction forming a
circle.
▪ A singly linked list is a linear data structure where each element (node) is
a separate object.
Tail
Node< T >
data nextNode
Field nextNode references a Node< T >
object, an object of the same <T> class .
Field data references the object of the <T> class .
Class List - definitions
• Class List represents a singly linked list.
• Each element ( we will call it a node ) of a list is comprising of two
items - the data and a reference to the next node.
• The last node has a reference to null. The entry point into a linked
list is called the head of the list. It should be noted that head is not
a separate node, but the reference to the first node. If the list is
empty then the head is a null reference.
• The number of nodes in a list is not fixed and can grow and shrink on
demand.
• In Java we are allowed to define a class (say, B) inside of another class
(say, A). The class A is called the outer class, and the class B is called the
inner class. The purpose of inner classes is purely to be used internally as
helper classes.
• The List class is the outer class and the Node class is the inner class.
4
Class List - methodsN Method’s name Method’s description
1 List() Constructor builds an empty linked list .
2 boolean isEmpty() Returns true if this list is empty and false
otherwise.
3 Node<T> getFirst() Returns the reference to first element in
this list. If list is empty returns null.
4 Node<T> insert(Node<T>
pos, T x)
Inserts the type T element x after the
specified position pos in this list and
returns the reference to inserted element
x.
5 Node<T> remove(Node<T>
pos)
Removes the first occurrence of the
specified element pos in this list and
returns the next element position.
We assume that pos != null.
6 String to String() Returns the string representation of
linked list.5
Outer class List - UML diagram
List<T>
Node<T> first
List()
boolean isEmpty()
Node<T> getFirst()
Node<T> insert(Node<T> pos, T x)
Node<T> remove(Node<T> pos)
String toString()
Class name
Class variable
Class methods
Constructor
6
Inner class Node - UML diagram
Node<T>
private T data
private Node<T> nextNode
Node(T x)
Node( T data, Node<T> nextNode )
T getData()
Node<T> getNext()
Void setData( T data)
Void setNext(Node<T> nextNode)
String toString()
Constructors
Class variables
Class methods
Class name
Class List - basic operations
8
addFirst : The method creates a node ( “C” ) and prepends it
at the beginning of the list.
9
Class List - basic operations
addLast: The method appends the node ( “S” ) to the end of the list.
10
Class List - basic operations
Inserting "after“:
Find a node containing "key" and insert a new node after it.
In the picture below, we insert a new node after “E”:
11
Class List - basic operations
Deletion:
Find a node containing "key" and delete it.In the picture below we delete a node containing “ A “
12
Class List - basic operations
Traversing:
Start with the head and access each node until you reach null.
Do not change the head reference !
Class List - implementationpublic class List<T>
{
private Node<T> first; // class List attribute
public List() {
this.first = null;
} // class List constructor
public Node<T> getFirst() {
return this.first;
} // getFirst
public boolen isEmpty() {
return this.first == null;
} // isEmpty
public String toString() {
String str = “ [ “;
Node<T> pos = this.first;
while(pos != null) {
str = str + pos.getData(); // class Node<T> method
if(pos.getNext() != null)
str = str + ”, ”;
pos = pos.getNext();
} // while
str = str + “]”;
return str;
} // toString
13
Class List – implementation,cont.public Node<T> insert(Node<T> pos, T x) {
Node<T> q = new Node<T>(x); // creating new node
if( pos == null ) {
q.setNext(this.first);
this.first = q; // first element in the list
}
else {
q.setNext(pos.getNext());
pos.setNext(q);
}
return q;
} // insert
public Node<T> remove(Node<T> pos) {
if( this.first == pos ) {
this.first = pos.getNext(); // remove first node
return this.first;
}
else {
Node<T> prev = this.first;
while(prev.getNext() != pos) // searching pos reference
prev = prev.getNext();
prev.setNext(pos.getNext());
return prev.getNext();
}
} // remove
} // class List
Note: Class Node<T>
methods
14
Class List - testThis program reads the names of 10 students ,builds linked list and prints the names
which begins with an ‘A’ character.
public static void main(String args[ ])
{
List<String> studNames = new List<String>();
Node<String> last = null;
for(int i = 0; i < 10; i++)
{
System.out.println(“ Enter student name “);
String name = reader.next();
last = studNames.insert(last,name);
} // for
Node<String> p = studNames.getFirst();
while(p != null ) {
if( p.getData().charAt(0) == ‘A’)
System.out.println(p.getData());
p = p.getNext();
} //while
} // main
15
public Node<T> insert(Node<T> pos, T x)
{
Node<T> q = new Node<T>(x);
if( pos == null )
{
q.setNext(this.first);
this.first = q; // first element in the list
}
else
{
q.setNext(pos.getNext());
pos.setNext(q);
}
return q;
} // insert
Class List – using external methodspublic static void nameA(Node<String> p)
{
while(p != null ) {
if( p.getData().charAt(0) == 'A') // getData from Node class, charAt() from String class
System.out.println(p.getData());
p = p.getNext();
} // while
} // nameA
public static void main(String args[ ])
{
List<String> studNames = new List<String>();
Node<String> last = null;
for(int i = 0; i < 10; i++) {
System.out.println(“ Enter student name “);
String name = reader.next();
last = studNames.insert(last,name);
} // for
Node<String> pl = studNames.getFirst();
nameA(pl); // calling method nameA from main method
} // main
16
External methods – “what is” questions
17
1. What is the output for the next program giving the following linked list?
public static void what(List<Integer> list)
{
Node<Integer> a = list.getFirst();
Node<Integer> b = list.getFirst();
while (b != null )
{
Node<Integer> temp = a;
a = a.getNext();
b = b.getNext();
list.remove(temp);
if (b != null)
b = b.getNext();
} // while
} // what
2. What is the purpose of the what method ?
public static void main(String[ ] args) {
List<Integer> ls = new List<Integer>();
Node<Integer> last = null;
System.out.print(" enter an integer -> ");
int x = reader.nextInt();
while ( x != 777) {
last = ls.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} // while
System.out.println(ls);
what(ls); // calling what method
System.out.println(ls);
} // main
“what is” questions - trace
18
b
a
temp a
b b
list
a
b
temp
b
b != null -> T
b != null -> T
public static void what(List<Integer> list) {
Node<Integer> a = list.getFirst();
Node<Integer> b = list.getFirst();
while (b != null ) {
Node<Integer> temp = a;
a = a.getNext();
b = b.getNext();
list.remove(temp);
if (b != null)
b = b.getNext(); } // while
} // what
“what is” questions - solution
19
enter an integer -> 1
enter an integer -> 2
enter an integer -> 3
enter an integer -> 4
enter an integer -> 777
[ 1, 2, 3, 4 ]
[ 3, 4 ]
Linked list values
sentinel
List before calling
what
List after calling what
The what method
removes the first half
giving in the linked list.
output
Class List methods - example1This program reads the coordinates of 10 points, builds linked list of Point type
and prints the coordinates of points which their value sums up to 20.
public static void main(String args[ ])
{
List<Point> ls = new List<Point>();
Node<Point> last = null;
for( int i = 0; i < 10; i++)
{
System.out.print(" enter X-> ");
int x = reader.nextInt();
System.out.print(" enter Y-> ");
int y = reader.nextInt();
last = ls.insert( last, new Point(x,y) );
} // for
System.out.println(ls);
printP20(ls); // calling external method (next slide)} // main
Building Point type linked list
Creating Point type linked list
20
Class List - method printP20public static void printP20(List<Point> lst)
{
Node<Point> pos = lst.getFirst();
while( pos != null ) {
Point point = pos.getData();
if( point.getX() + point.getY() <= 20)
System.out.println(point);
pos = pos.getNext();
} // while
} // printP20Class Node
method
Class Point
methods
Class List method
21
method main - what’s different?
public static void main(String args[ ])
{
List<Point> ls = new List<Point>();
for( int i = 0; i < N; i++)
{
System.out.print(" enter X-> ");
int x = reader.nextInt();
System.out.print(" enter Y-> ");
int y = reader.nextInt();
ls.insert( null, new Point(x,y) );
} // for
System.out.println(ls);
printP20(ls); // calling external method
} // main
public static void main(String args[ ])
{
List<Point> ls = new List<Point>();
Node<Point> last = null;
for( int i = 0; i < N; i++)
{
System.out.print(" enter X-> ");
int x = reader.nextInt();
System.out.print(" enter Y-> ");
int y = reader.nextInt();
last= ls.insert( last, new Point(x,y) );
} // for
System.out.println(ls);
printP20(ls); // calling external method
} // main
22
method main output, N = 3enter X-> 1enter Y-> 2enter X-> 3enter Y-> 4enter X-> 5enter Y-> 6[ x= 1.0 y= 2.0, x= 3.0 y= 4.0, x= 5.0 y= 6.0]
x= 1.0 y= 2.0x= 3.0 y= 4.0x= 5.0 y= 6.0
enter X-> 1enter Y-> 2enter X-> 3enter Y-> 4enter X-> 5enter Y-> 6[ x= 5.0 y= 6.0, x= 3.0 y= 4.0, x= 1.0 y= 2.0]
x= 5.0 y= 6.0x= 3.0 y= 4.0x= 1.0 y= 2.0
public Node<T> insert(Node<T> pos, T x)
{
Node<T> q = new Node<T>(x);
if( pos == null )
{
q.setNext(this.first);
this.first = q; // first element in the list
} // if
else
{
q.setNext(pos.getNext());
pos.setNext(q);
} // else
return q;
} // insert
23
This method checks if the linked list of String type is sorted
public static boolean isSorted(List<String> lst)
{
Node<String> pos = lst.getFirst();
while(pos != null)
{
if( pos.getNext() != null )
if( pos.getData().compareTo(pos.getNext().getData() ) > 0 )
return false;
pos = pos.getNext();
} // while
return true;
} // isSorted
24
Class List methods – example2
Example2 – main and executions
public static void main(String args[ ])
{
List<String> ls = new List<String>();
Node<String> last = null;
for(int i = 1; i < 5; i++)
{
System.out.print(" enter the string ");
String x = reader.next();
last = ls.insert(last, x);
} // for
System.out.println(ls);
if(isSorted(ls))
System.out.println("YES");
else
System.out.println("NO");
} // main
enter the string hello
enter the string hi
enter the string word
enter the string bee
[ hello, hi, word, bee ]
NO
enter the string bee
enter the string hello
enter the string hi
enter the string word
[ bee, hello, hi, word ]
YES
25
Class List methods - example 3
public static void remDuplications(List<Character> lst)
{
Node<Character> pos1= lst.getFirst(), pos2;
while( pos1 != null )
{
char ch = pos1.getData();
pos2 = pos1.getNext();
while( pos2 != null )
{
if(pos2.getData() == ch)
pos2 = lst.remove(pos2);
else
pos2 = pos2.getNext();
} // inner while
pos1 = pos1.getNext();
} // outer while
} // remDuplications
26
This method removes all duplications in Character type linked list
s a b aa z nulllst
sa b z nulllst
Example3 – main and executionspublic static void main (String[ ] args)
{
List<Character> ls = new List<Character>();
Node<Character> last = null;
System.out.print( " enter the character -> “ );
char x = reader.next().charAt(0);
while ( x != ‘*’ ) {
last = ls.insert(last, x);
System.out.print( " enter the character -> “ );
x = reader.next().charAt(0);
} // while
System.out.println(ls);
remDuplications(ls);
System.out.println(ls);
} // main
27
enter the character -> a
enter the character -> s
enter the character -> a
enter the character -> b
enter the character -> a
enter the character -> z
enter the character -> *
[ a, s, a, b, a, z ]
[ a, s, b, z ]
sentinel
Merging two linked list
• Write a Java program that contains a method with the capability to merge two integer type sorted linked lists ( lst1 and lst2 ) .
• The merged result should be in the third linked list ( lst3 ) that is in sorted order. Do not destroy the original lists.
• Your program should output the content of three linked lists to show the program performs properly.
28
Method merge2Listspublic static List<Integer> merge2Lists(List<Integer> lst1, List<Integer> lst2) {
Node<Integer> pos1 = lst1.getFirst(), pos2 = lst2.getFirst(), pos3 = null;
List<Integer> lst3 = new List<Integer>();
while( pos1 != null && pos2 != null ) {
if( pos1.getData() > pos2.getData() ) {
pos3 = lst3.insert(pos3,pos2.getData());
pos2 = pos2.getNext();
}
else {
pos3 = lst3.insert(pos3,pos1.getData());
pos1 = pos1.getNext();
} // if
} // while
while(pos1 != null) {
pos3 = lst3.insert(pos3,pos1.getData());
pos1 = pos1.getNext();
} // while
while(pos2 != null) {
pos3 = lst3.insert(pos2,pos2.getData());
pos1 = pos2.getNext();
} // while
return lst3;
} // merge2List 29
merge2Lists – main and executionspublic static void main(String[ ] args) {
List<Integer> lst1 = new List<Integer>(), lst2 = new List<Integer>();
Node<Integer> last = null;
System.out.print(" enter an integer -> ");
int x = reader.nextInt();
while ( x != 777) {
last = lst1.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} // while
last = null;
System.out.print(" enter an integer -> ");
x = reader.nextInt();
while ( x != 777) {
last = lst2.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} // while
List<Integer> lst3 = merge2Lists(ls1,ls2);
System.out.println(ls1);
System.out.println(ls2);
System.out.println(ls3);
} // main30
enter an integer -> 1
enter an integer -> 2
enter an integer -> 5
enter an integer -> 8
enter an integer -> 9
enter an integer -> 777
enter an integer -> 3
enter an integer -> 4
enter an integer -> 7
enter an integer -> 777
[ 1, 2, 5, 8, 9 ] [ 3, 4, 7 ] [ 1, 2, 3, 4, 5, 7, 8, 9 ]
lst1
lst2
sentinel
sentinel
output
Class List methods - example 4
31
This method calculates the number of different values in the integer type linked list.
public static int countDifItems(List<Integer> list) {
Node<Integer> temp, pos = list.getFirst();
int count = 0; // number of different values
while(pos != null) {
temp = pos.getNext();
boolean found = false; // not found
while(temp != null) {
if(temp.getData() == pos.getData()) {
found = true;
break;
} // if
temp = temp.getNext();
} // inner while
if( !found )
count++;
pos = pos.getNext();
} // outer while
return count;
} // countDifItems
3
Example4 – main and executions
32
public static void main(String[ ] args)
{
List<Integer> ls = new List<Integer>();
Node<Integer> last = null;
System.out.print(" enter an integer -> ");
int x = reader.nextInt();
while ( x != 777)
{
last = ls.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} // while
System.out.println(ls);
System.out.println(“Count = " + countDifItems(ls));
} // main
enter an integer -> 1
enter an integer -> 2
enter an integer -> 1
enter an integer -> 2
enter an integer -> 5
enter an integer ->
777
[ 1, 2, 1, 2, 5 ]
Count = 3
Class List methods - example 5
33
This method checks if the linked list of integer type is circular linked list
public static boolean checkCircle(List<Integer> list)
{
Node<Integer> a = list.getFirst();
Node<Integer> b = list.getFirst();
while ( b != null )
{
a = a.getNext();
b = b.getNext();
if ( b != null )
b = b.getNext();
else
return false;
if (a == b)
return true;
} // while
return false;
} // checkCircle
Tail
Example5 – main and executions
34
public static void main(String[ ] args) {
List<Integer> ls = new List<Integer>();
Node<Integer> last = null;
System.out.print(" enter an integer -> ");
int x = reader.nextInt();
while ( x != 777) {
last = ls.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} //while
System.out.println(ls);
if(checkCircle(ls))
System.out.println("YES");
else
System.out.println("NO");
} // main
enter an integer -> 1
enter an integer -> 2
enter an integer -> 3
enter an integer -> 4
enter an integer -> 5
enter an integer -> 777
[ 1, 2, 3, 4, 5 ]
YES
/* building circular linked list */
Node<Integer> pos = ls.getFirst();
Node<Integer> first = ls.getFirst();
while(pos.getNext() != null )
pos = pos.getNext();
pos.setNext(first);
enter an integer -> 1
enter an integer -> 2
enter an integer -> 3
enter an integer -> 4
enter an integer -> 5
enter an integer -> 777
[ 1, 2, 3, 4, 5 ]
NO
Class List recursive method1
35
This method tests if the number which passed as parameter exists in the
linked list of integer type.
public static boolean what1(List<Integer> lst, int num)
{
boolean ans; // returned value
int temp; // help variable
if( lst.isEmpty() )
ans = false;
else
{
temp = lst.getFirst().getData();
lst.remove(lst.getFirst());
ans = (temp == num) || what1(lst,num);
lst.insert(null, temp);
} // if
return ans;
} // what
Recursive methods1 debugging
36
public static boolean what1(List<Integer> lst, int num)
{
boolean ans; // returned value
int temp; // help variable
if( lst.isEmpty() )
ans = false;
else
{
temp = lst.getFirst().getData();
lst.remove(lst.getFirst());
ans = (temp == num) || what1(lst,num);
System.out.println("before insert temp“ + lst);
lst.insert(null, temp);
System.out.println(“after insert temp“ + lst);
} // else
return ans;
} // what1
enter an integer -> 1
enter an integer -> 2
enter an integer -> 3
enter an integer -> 777
[ 1, 2, 3 ]
enter search number -> 5
before insert temp [ ]
after insert temp [ 3 ]
before insert temp [ 3 ]
after insert temp [ 2, 3 ]
before insert temp [ 2, 3 ]
after insert temp [ 1, 2, 3 ]
NO
enter an integer -> 1
enter an integer -> 2
enter an integer -> 3
enter an integer -> 777
[ 1, 2, 3 ]
enter search number -> 2
before insert temp [ 3 ]
after insert temp [ 2, 3 ]
before insert temp [ 2, 3 ]
after insert temp [ 1, 2, 3 ]
YES
Linked list recursive method2
public static int what2(Node<Integer> lst)
{
if ( lst == null )
return 0;
Node<Integer> pos = lst.getNext();
int temp = what2(pos);
if( !(temp % 2 == 0) )
{
System.out.println( "temp= “ + temp);
System.out.println(pos.getData());}
return temp + 1;
} // what237
This method take the reference to first element in the singly linked list as parameter.
What is the output of the method for the following linked list ?
recursive method2 - solution
38
[ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
temp = 1
9
temp = 3
7
temp = 5
5
temp = 7
3
what2 = 9
public static void main(String[ ] args)
{
List<Integer> ls = new List<Integer>();
Node<Integer> last = null;
System.out.print(" enter an integer -> ");
int x = reader.nextInt();
while ( x !=777)
{
last = ls.insert(last, x);
System.out.print(" enter an integer -> ");
x = reader.nextInt();
} // while
System.out.println(ls);
Node<Integer> first = ls.getFirst();
System.out.println("what2 = " + what2(first));
} // main
This will produce the next output :
Method what2 returns the number of elements in the singly
linked list.
Class List methods - exam question
39
Write the method:
public static int MaxSubList( List<Character> lst, char x, char y )
The method receives the length of the largest sub-list, which can be found between characters x and y.
If such sub-list is not found the method receives 0.
For example:
If we have the following list: lst = 'a', 'd', 'z', 'a', 't', 't', 'a', 'y', 'w‘
The method MaxSubList(lst,'z','a') receives the value 5 ( lst = z, a, t, t, a ).
The method MaxSubList(lst,'w','w') receives the value 1.
The method MaxSubList(lst,'a','k') receives the value 0.
Exam question - solutionpublic static int MaxSubList ( List<Character> lst, char x, char y ) {
Node<Character> pos = lst.getFirst();boolean start = false; // found x valueint maxLen = 0; // largest sub-list lengthint curLen = 0; // current sub-list lengthwhile (pos != null) {
if (pos.getData() == x(
{start = true;break;
} // ifpos = pos.getNext();
} // whileif (x == y)
curLen = 1;while (pos != null && start) {
if (pos.getData() == y){
maxLen += curLen;curLen = 0;
} // ifcurLen++;pos = pos.getNext();
} // whilereturn maxLen;
} // MaxSubList
40
