Welcome to CSL 201 Data Structures

Transcription

1 Welcome to CSL 201 Data Structures Narayanan (CK) C Krishnan Department of Computer Science and Engineering IIT Ropar

2 Administrative Trivia Course Structure n (5 credits) Class Timings n Monday n Tuesday n Wednesday Lab hours n Thursday Teaching Assistant n Yayati Gupta (yayati.gupta@iitrpr.ac.in) Office Hours n n Instructor M,T,W immediately after class TA during lab hours Course Google group csl201f15@iitrpr.ac.in Pre-registered students have already been added n other students send to the instructor Pseudonym n n 5 character July 31, 5.00pm 2

3 Reference Material Data Structures and Algorithms in Java Goodrich, Tamasia and Goldwasser 6 th edition Introduction to Algorithms Cormen, Leiserson, Rivest, Stein 3 rd edition Fundamentals of Data Structures Horowitz Sahni 3

4 Learning every week 4

5 Tentative Course Schedule 5

6 Quizzes 30% Almost every alternate Thursday n n am L2 Q3 and Q6 will also have programming problems Cover material discussed from the previous quiz till the current week Duration 30-45m Rest of the time problem solving/tutorial Quiz Number Date Q1 Aug 6 Q2 Aug 20 Q3 Sep 3 Q4 Oct 1 Q5 Oct 15 Q6 Oct 29 Q7 Nov 12 6

7 Labs 20% Due almost every alternate Friday 11.55pm Programming Assignments TA is available for any assistance. Java programming language n Introductory Tutorial - July am in L2 Lab Number Date L1 Aug 14 L2 Aug 28 L3 Sep 4 L4 Sep 24 L5 Oct 8 L6 Oct 22 L7 Nov 5 L8 Nov 19 7

8 Grading Scheme Tentative Breakup n Quizzes (6-7) 30% n Labs (6-8) 20% n Mid-Semester Exam 25% n End-Semester Exam 25% Passing Criteria: A student has to secure an overall score of 40(out of 100) and a combined score of 60(out of 200) in the exams to pass the course 8

9 Attendance Bonus 1% No mandatory attendance Encourage you to attend classes Attendance will be taken during every class 1% will count towards the final score n Borderline grades will have an edge 9

10 Honor Code Encourage to form study groups to review class lectures/textbook material n Group discussions are encouraged Unless explicitly stated all quizzes and labs n are to be done individually. n web trawled code or code copied from classmates is strictly forbidden. Any infraction will be dealt in severest terms n Direct F grade in the course. I reserve the right to question you, if I suspect any misconduct in any submission. 10

11 Course Website csl201/csl201.html All class related material will be accessible from the course webpage. 11

12 Data Structures What are data structures? 12

13 Data Structures What are data structures? n a way to organize data n easier access/manipulate to data Topics for the next couple of weeks n Concrete Data Structures w Arrays and Linked Lists n Algorithmic Analysis n Recursion 13

14 Arrays 2014 Goodrich, Tamassia, Goldwasser Arrays 14

15 Java Example: Game Entries A game entry stores the name of a player and her best score so far in a game 2014 Goodrich, Tamassia, Goldwasser Arrays 15

16 Java Example: Scoreboard Keep track of players and their best scores in an array, board n n The elements of board are objects of class GameEntry Array board is sorted by score 2014 Goodrich, Tamassia, Goldwasser Arrays 16

17 Array Definition An array is a sequenced collection of variables all of the same type. Each variable, or cell, in an array has an index, which uniquely refers to the value stored in that cell. The cells of an array, A, are numbered 0, 1, 2, and so on. Each value stored in an array is often called an element of that array. A n i 2014 Goodrich, Tamassia, Goldwasser Arrays 17

18 Array Length and Capacity Since the length of an array determines the maximum number of things that can be stored in the array, we will sometimes refer to the length of an array as its capacity. In Java, the length of an array named a can be accessed using the syntax a.length. Thus, the cells of an array, a, are numbered 0, 1, 2, and so on, up through a.length 1, and the cell with index k can be accessed with syntax a[k]. a n k 2014 Goodrich, Tamassia, Goldwasser Arrays 18

19 Declaring Arrays (first way) The first way to create an array is to use an assignment to a literal form when initially declaring the array, using a syntax as: The elementtype can be any Java base type or class name, and arrayname can be any valid Java identifier. The initial values must be of the same type as the array Goodrich, Tamassia, Goldwasser Arrays 19

20 Declaring Arrays (second way) The second way to create an array is to use the new operator. n However, because an array is not an instance of a class, we do not use a typical constructor. Instead we use the syntax: new elementtype[length] length is a positive integer denoting the length of the new array. The new operator returns a reference to the new array, and typically this would be assigned to an array variable Goodrich, Tamassia, Goldwasser Arrays 20

21 Arrays of Characters or Object References An array can store primitive elements, such as characters. An array can also store references to objects Goodrich, Tamassia, Goldwasser Arrays 21

22 Adding an Entry To add an entry e into array board at index i, we need to make room for it by shifting forward the n - i entries board[i],, board[n 1] board board board n i n i e i n 2014 Goodrich, Tamassia, Goldwasser Arrays 22

23 Java Example 2014 Goodrich, Tamassia, Goldwasser Arrays 23

24 Removing an Entry To remove the entry e at index i, we need to fill the hole left by e by shifting backward the n - i - 1 elements board[i + 1],, board[n 1] board board board e i n n i n i 2014 Goodrich, Tamassia, Goldwasser Arrays 24

25 Java Example 2014 Goodrich, Tamassia, Goldwasser Arrays 25

26 Sorting an Array Insertion Sort Code Fragment 3.6 Arrays 26

27 Insertion Sort - Example cur no move C B 0 C D A E H G F no move D B C D A E H G F move move A insert move A B C D E H G F no move B 0 C D E H G F B C D E H G F E A B C D E H G F no move H A B C D E H G F move no move G insert Figure 3.5 G A 0 B C D E H F A B C D E H F move move no move F insert F A B C D E G H A B C D E G H A B C D E G H A 0 B 1 C D E F G H Done! Arrays 27

28 Drawbacks of Arrays Fixed capacity Insertions and Deletions involve many shifting operations Arrays 28

29 Singly Linked Lists Singly Linked Lists 29

30 Singly Linked List head A singly linked list is a concrete data structure consisting of a sequence of nodes, starting from a head pointer Each node stores n n element link to the next node element next node A B C D 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 30

31 A Nested Node Class 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 31

32 Accessor Methods 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 32

33 Inserting at the Head Allocate new node Insert new element Have new node point to old head Update head to point to new node 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 33

34 Inserting at the Tail Allocate a new node Insert new element Have new node point to null Have old last node point to new node Update tail to point to new node 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 34

35 Java Methods 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 35

36 Removing at the Head Update head to point to next node in the list Allow garbage collector to reclaim the former first node 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 36

37 Java Method 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 37

38 Removing at the Tail Removing at the tail of a singly linked list is not efficient! There is no constant-time way to update the tail to point to the previous node 2014 Goodrich, Tamassia, Goldwasser Singly Linked Lists 38

39 Doubly Linked Lists Doubly Linked Lists 39

40 Doubly Linked List A doubly linked list can be traversed forward and backward Nodes store: n element n n link to the previous node link to the next node Special trailer and header nodes prev element next node header nodes/positions trailer elements 2014 Goodrich, Tamassia, Goldwasser Doubly Linked Lists 40

41 Insertion Insert a new node, q, between p and its successor. p A B C p A B q C p q X A B X C 2014 Goodrich, Tamassia, Goldwasser Doubly Linked Lists 41

42 Deletion Remove a node, p, from a doubly linked list. p A B C D A B C p D A B C 2014 Goodrich, Tamassia, Goldwasser Doubly Linked Lists 42

43 Doubly-Linked List in Java 2014 Goodrich, Tamassia, Goldwasser Doubly Linked Lists 43

44 Doubly-Linked List in Java, Goodrich, Tamassia, Goldwasser Doubly Linked Lists 44

45 Doubly-Linked List in Java, Goodrich, Tamassia, Goldwasser Doubly Linked Lists 45

46 Doubly-Linked List in Java, Goodrich, Tamassia, Goldwasser Doubly Linked Lists 46