CP222 Computer Science II. Linked Lists

Transcription

1 CP222 Computer Science II Linked Lists

2 Facebook data and Cambridge Analytica Tech News!

3 Tech News! Facebook data and Cambridge Analytica Amazon now delivering Prime to car trunks

4 Getting Help Fei CS Paraprof Lab time: 1pm-2pm daily QRC Tutors Daily 6-8pm My office hours: 2pm-3pm Mon-Thurs

5 Data Structure: BAG A simple collection of items. Removing and indexing are not supported. Methods void add(item item) boolean isempty() int size() add an item check if bag is empty get the number of items

6 MyBag.java (static array implementation)

7 Peak Baggers?

8 Linked Structures and Lists Review abstract data type How can we create dynamically sized data structures? How can we implement a simple list?

9 A Data Structure public class RoboticOverlord { private String name; private int heightinmeters; private int numlasers; private short numfacebookfriends; }

10 A Data Structure public class RoboticOverlord { private String name; private int heightinmeters; private int numlasers; private short numfacebookfriends; } Great for solving problems involving robotic overlords. Pretty much useless for every other kind of problem.

11 Collections Generic data structures Can hold different kinds of objects Can be used to solve different kinds of problems

12 Collections Generic data structures Can hold different kinds of objects Can be used to solve different kinds of problems Each collection can have its own structure Structure is not tied to a particular programming language

13 Abstract Data Type A logical data type abstracted from implementational details

14 Abstract Data Type A logical data type abstracted from implementational details E.g. A sequential list Add items to the end of the list Retrieve an item stored at a particular index Remove an item Etc.

15 Data Structure (ADT in Action) A data structure is an actual implementation of an ADT E.g. Java's ArrayList class is a data structure that implements a sequential list abstraction There are other possible implementations of the sequential list abstraction

16 Suppose you are a hoarder and you would like to collect and store digits of π in order Program

17 Possible Solution

18 Possible Solution array 3

19 Possible Solution array 3 1

20 Possible Solution array 3 1 4

21 Possible Solution Out of space! array

22 PiHoarder.java with arrays can t handle an arbitrary number of digits. We need a data structure that can grow dynamically when necessary.

23 Data Structure: Linked List An ordered, sequential collection of items. Can grow in size dynamically.

24 Data Structure: Linked List An ordered, sequential collection of items. Can grow in size dynamically. Methods void add(item item) void remove(item item) int size() Item getitem(int index) void insert(int index) add an item at the end find and remove an item get the number of items retrieve a specific item insert new item at index

25 Java API: LinkedList Class

26 Linked List Implementation?

27 A Reference/Link/Pointer public class Student { private String name; private float gpa; }

28 A Reference/Link/Pointer public class Student { private String name; private float gpa; } This name instance variable is really a reference or link to a String object. This means it just stores a memory address where the String resides.

29 A Self Reference public class Student { private String name; private float gpa; private Student bestfriend; }

30 A Self Reference public class Student { private String name; private float gpa; private Student bestfriend; } Now each Student has a link to another Student. This works because it's really just another memory address.

31 Students can be linked together student1 student2 student3

32 Objects of generic types (T) can be linked together T1 T2 T3

33 Java Generics We want our List to work with all kinds of elements, right? List<String> or List<Student> or... Just like Java's ArrayList<String>

34 public class List<T> { } Generic List public void add(t newelement) {... } public T get(int index) {... }

35 LinkedList Implementation

36 LinkedList Nodes Two components: 1. A link to the next node 2. The element itself

37 LinkedList Implementation First Last

38 LinkedList: add First Last

39 LinkedList: add First Last

40 LinkedList: insert First Last

41 LinkedList: insert First Last

42 LinkedList: insert First Last

43 LinkedList: remove First Last

44 LinkedList: remove First Last

45 LinkedList: remove First Last

46 Possible Solution Out of space! array

47 Linked List Implementation? LinkedList.java

48 List implemented with an array

49 List implemented with an array Being used Unused

50 ArrayList: add

51 ArrayList: insert

52 ArrayList: insert Shift required!

53 ArrayList: insert

54 ArrayList: insert

55 ArrayList: remove

56 ArrayList: remove

57 ArrayList: remove Shift required!

58 ArrayList: remove

59 ArrayList: grow Add or insert, but array is full!

60 ArrayList: grow

61 ArrayList: grow Copied from old array

62 ArrayList: grow Add new element

63 Doubly LinkedList Implementation First Last

64 Doubly LinkedList: insert First Last

65 Doubly LinkedList: insert First Last

66 Doubly LinkedList: insert First Last

67 Group Programming Write an insert method for a doubly linked list - Assume each node has two links: next and previous - Assume you want to insert the new node after a node called existingnode

68 BREAK!