+ - 0:00:00
Notes for current slide
Notes for next slide

CSCI-UA 102

Data Structures


Lists (Part 3)

Instructor: Joanna Klukowska


Copyright 2020 Joanna Klukowska. Unless noted otherwise all content is released under a
Creative Commons Attribution-ShareAlike 4.0 International License.
Background image by Stewart Weiss

1/27

Other Flavors of a Linked List

2/27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.
3/27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.

In a doubly linked list there is a double connection between the nodes: each node has a reference to the node that follows and to the node that precedes it.

4/27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.

In a doubly linked list there is a double connection between the nodes: each node has a reference to the node that follows and to the node that precedes it.

In a circular linked list the last node is connected back to the first node (instead of having its reference set to null). Circular linked lists could be singly- or doubly linked.

5/27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list

6/27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

7/27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
8/27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
  • Some operations become more efficient. For example, removing the last node, since tail.prev provides the reference to the node before last and it does not require iterating through the entire list.
9/27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
  • Some operations become more efficient. For example, removing the last node, since tail.prev provides the reference to the node before last and it does not require iterating through the entire list.
  • Java's LinkedList<E> class uses a doubly linked list implementation.
10/27

© Joanna Klukowska. CC-BY-SA.

Circular Linked List

circular singly linked list

Circular singly linked list.

  • there is a single reference in each node pointing to the next node
  • the last node's reference, points back to the first node
11/27

© Joanna Klukowska. CC-BY-SA.

Circular Linked List

circular singly linked list

Circular singly linked list.

  • there is a single reference in each node pointing to the next node
  • the last node's reference, points back to the first node

circular doubly linked list

Circular doubly linked list.

  • there two references between a pair of any nodes: one pointing forward, the other pointing back
  • the last node's next reference, points back to the first node
  • the first node's prev reference, points to the last node
12/27

Defining and Iterator for our LinkedList

13/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

An iterator is an object that allows us to traverse a collection (data structure) and visit each element exactly once.

Objective: be able to return the next element fast, i.e., in O(1), so that the entire collection can be traversed in O(N) time.

14/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}
15/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method
  • using an iterator
16/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method O(N)
  • using an iterator O(N)
17/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}
18/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method
  • using an iterator
19/27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method O(N2) (because the get() method takes O(N) time)
  • using an iterator O(N)
20/27

© Joanna Klukowska. CC-BY-SA.

How to Implement an Iterator for a Linked List

Here is a very simple iterator to satisfies the Iterator<E> interface (well, almost):

private class Itr implements Iterator<E> {
    private Node current = head;
    public boolean hasNext() {
        return current != null;
    }
    public E next()
    {
        E tmp = current.data;
        current = current.next;
        return tmp;
    }
}
21/27

© Joanna Klukowska. CC-BY-SA.

How to Implement an Iterator for a Linked List

Here is a very simple iterator to satisfies the Iterator<E> interface (well, almost):

private class Itr implements Iterator<E> {
    private Node current = head;
    public boolean hasNext() {
        return current != null;
    }
    public E next()
    {
        E tmp = current.data;
        current = current.next;
        return tmp;
    }
}

and to make the list itself Iterable, we need to add the following method to the list

public Iterator<E> iterator() {
    return new Itr();
}
22/27

Examples and Things to Think About

23/27

© Joanna Klukowska. CC-BY-SA.

LinkedList<E> source code

Study the source code of a doubly linked list implementation provided by the LinkedList<E> class in Java.

You should be able to understand what it does and why.

24/27

© Joanna Klukowska. CC-BY-SA.

Is it circular?

Given a reference to the first node, i.e. head determine if the list is circular or not.

  • case 1: assume that there is a tail reference pointing to the last node
  • case 2: assume that there is no tail reference

What is the performance of these two methods.

25/27

© Joanna Klukowska. CC-BY-SA.

Does it have a loop?

Given a reference to the first node, i.e. head determine if the list has a loop or not (a loop in a list means that the last node points back to another node in the list).

list with a loop, and without a loop

26/27

© Joanna Klukowska. CC-BY-SA.

What will this code output?

Assume that we execute the following code fragment. What is the output?

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
Iterator<String> itr = aL.iterator();
System.out.println(itr.next() );
itr.next();
System.out.println(itr.next() );
Iterator<String> itr1 = aL.iterator();
Iterator<String> itr2 = aL.iterator();
System.out.println(itr1.next());
System.out.println(itr2.next());
System.out.println(itr.next());
27/27

CSCI-UA 102

Data Structures


Lists (Part 3)

Instructor: Joanna Klukowska


Copyright 2020 Joanna Klukowska. Unless noted otherwise all content is released under a
Creative Commons Attribution-ShareAlike 4.0 International License.
Background image by Stewart Weiss

1 / 27

Other Flavors of a Linked List

2 / 27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.
3 / 27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.

In a doubly linked list there is a double connection between the nodes: each node has a reference to the node that follows and to the node that precedes it.

4 / 27

© Joanna Klukowska. CC-BY-SA.

Other Flavors of a Linked List

The list that we discussed extensively is a singly linked list. In that list

  • there is a single reference from a node to the node that follows, and
  • the last node's reference is set to null.

In a doubly linked list there is a double connection between the nodes: each node has a reference to the node that follows and to the node that precedes it.

In a circular linked list the last node is connected back to the first node (instead of having its reference set to null). Circular linked lists could be singly- or doubly linked.

5 / 27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list

6 / 27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

7 / 27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
8 / 27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
  • Some operations become more efficient. For example, removing the last node, since tail.prev provides the reference to the node before last and it does not require iterating through the entire list.
9 / 27

© Joanna Klukowska. CC-BY-SA.

Doubly Linked List

doubly linked list 

class Node<E> {
    E data;
    Node<E> next;
    Node<E> prev;
}

nodes in doubly linked list

  • Working with a doubly linked list is very similar to working with a singly linked list, but there are twice as many references to keep track of.
  • Some operations become more efficient. For example, removing the last node, since tail.prev provides the reference to the node before last and it does not require iterating through the entire list.
  • Java's LinkedList<E> class uses a doubly linked list implementation.
10 / 27

© Joanna Klukowska. CC-BY-SA.

Circular Linked List

circular singly linked list

Circular singly linked list.

  • there is a single reference in each node pointing to the next node
  • the last node's reference, points back to the first node
11 / 27

© Joanna Klukowska. CC-BY-SA.

Circular Linked List

circular singly linked list

Circular singly linked list.

  • there is a single reference in each node pointing to the next node
  • the last node's reference, points back to the first node

circular doubly linked list

Circular doubly linked list.

  • there two references between a pair of any nodes: one pointing forward, the other pointing back
  • the last node's next reference, points back to the first node
  • the first node's prev reference, points to the last node
12 / 27

Defining and Iterator for our LinkedList

13 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

An iterator is an object that allows us to traverse a collection (data structure) and visit each element exactly once.

Objective: be able to return the next element fast, i.e., in O(1), so that the entire collection can be traversed in O(N) time.

14 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}
15 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method
  • using an iterator
16 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an ArrayList<E> object using an ordinary for loop and the get(index) method and using an iterator.

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < aL.size(); i++ ) {
    System.out.println(aL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = aL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method O(N)
  • using an iterator O(N)
17 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}
18 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method
  • using an iterator
19 / 27

© Joanna Klukowska. CC-BY-SA.

Why do we need iterators?

Here is an example of iterating over an LinkedList<E> object using an ordinary for loop and the get(index) method and using an iterator.

LinkedList<String> lL = new LinkedList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    lL.add(strings[i]);
}
System.out.println("Using for loop with .get() method" );
for (int i = 0; i < lL.size(); i++ ) {
    System.out.println(lL.get(i));
}
System.out.println("Using an iterator" );
Iterator<String> itr = lL.iterator();
itr = lL.iterator();
while (itr.hasNext()){
    System.out.println(itr.next() );
}

What is the performance of each method?

  • using or loop with .get() method O(N2) (because the get() method takes O(N) time)
  • using an iterator O(N)
20 / 27

© Joanna Klukowska. CC-BY-SA.

How to Implement an Iterator for a Linked List

Here is a very simple iterator to satisfies the Iterator<E> interface (well, almost):

private class Itr implements Iterator<E> {
    private Node current = head;
    public boolean hasNext() {
        return current != null;
    }
    public E next()
    {
        E tmp = current.data;
        current = current.next;
        return tmp;
    }
}
21 / 27

© Joanna Klukowska. CC-BY-SA.

How to Implement an Iterator for a Linked List

Here is a very simple iterator to satisfies the Iterator<E> interface (well, almost):

private class Itr implements Iterator<E> {
    private Node current = head;
    public boolean hasNext() {
        return current != null;
    }
    public E next()
    {
        E tmp = current.data;
        current = current.next;
        return tmp;
    }
}

and to make the list itself Iterable, we need to add the following method to the list

public Iterator<E> iterator() {
    return new Itr();
}
22 / 27

Examples and Things to Think About

23 / 27

© Joanna Klukowska. CC-BY-SA.

LinkedList<E> source code

Study the source code of a doubly linked list implementation provided by the LinkedList<E> class in Java.

You should be able to understand what it does and why.

24 / 27

© Joanna Klukowska. CC-BY-SA.

Is it circular?

Given a reference to the first node, i.e. head determine if the list is circular or not.

  • case 1: assume that there is a tail reference pointing to the last node
  • case 2: assume that there is no tail reference

What is the performance of these two methods.

25 / 27

© Joanna Klukowska. CC-BY-SA.

Does it have a loop?

Given a reference to the first node, i.e. head determine if the list has a loop or not (a loop in a list means that the last node points back to another node in the list).

list with a loop, and without a loop

26 / 27

© Joanna Klukowska. CC-BY-SA.

What will this code output?

Assume that we execute the following code fragment. What is the output?

ArrayList<String> aL = new ArrayList<>();
String [] strings = {"hello", "big", "pink", "cat"};
for (int i = 0; i < strings.length; i++) {
    aL.add(strings[i]);
}
Iterator<String> itr = aL.iterator();
System.out.println(itr.next() );
itr.next();
System.out.println(itr.next() );
Iterator<String> itr1 = aL.iterator();
Iterator<String> itr2 = aL.iterator();
System.out.println(itr1.next());
System.out.println(itr2.next());
System.out.println(itr.next());
27 / 27

Other Flavors of a Linked List

2 / 27
Paused

Help

Keyboard shortcuts

↑, ←, Pg Up, k Go to previous slide
↓, →, Pg Dn, Space, j Go to next slide
Home Go to first slide
End Go to last slide
Number + Return Go to specific slide
b / m / f Toggle blackout / mirrored / fullscreen mode
c Clone slideshow
p Toggle presenter mode
t Restart the presentation timer
?, h Toggle this help
Esc Back to slideshow
+ -
Notes for current slide
Notes for next slide
Paused

Help

Keyboard shortcuts

↑, ←, Pg Up, k Go to previous slide
↓, →, Pg Dn, Space, j Go to next slide
Home Go to first slide
End Go to last slide
Number + Return Go to specific slide
b / m / f Toggle blackout / mirrored / fullscreen mode
c Clone slideshow
p Toggle presenter mode
t Restart the presentation timer
?, h Toggle this help
Esc Back to slideshow