IT 4043 Data Structures and Algorithms. Budditha Hettige Department of Computer Science

Transcription

1 IT 4043 Data Structures and Algorithms Budditha Hettige Department of Computer Science 1

2 IT4043: Data Structures and Algorithms Lectures 30 Hours Practical /Tutorials 30 hours Assignment (30%) Practical Test (10 marks) Quizzes 4 (Get maximum 2 ) (10 x2 = 20 marks ) Total 30% Final Examination (70 %) 4 Questions (3 hours) (70%) Reference: 7/11/2015 Budditha Hettige (budditha@yahoo.com) 2

3 Syllabus Introduction to DSA Abstract Data Types List Operation Using Arrays Stacks Queues Recursion Link List Sorting Searching Algorithms Analysis 3

4 Introduction

5 Data Structure Data + Structure A data structure is an arrangement of data in a computer s memory (or sometimes on a disk). Example: arrays linked lists Stacks Queues binary trees 5

6 Algorithms Algorithms manipulate the data in these structures in various ways, such as searching for a particular data item and sorting the data. 6

7 Example: Algorithms for searching/sorting 7

8 Example Write a Java program enter 10 integer number in to an array Write 2 method findmin() and findmax() that returns smallest and largest value of the above data set. Write a method name finditem(int index) that return a value of the given array index

9 Data Structures and Algorithms for.. Real-world data storage A personnel record describes an actual human being An inventory record describes an existing car part or grocery item A financial transaction record describes, an actual check written to pay the electric bill. Programmer s tools Modeling Data Structures and Algorithms 9

10 Advantages & Disadvantages 10

11 Abstract Data Types (ADT)

12 Abstract Data Type (ADT) ADT is a collection of data and a set of operations that can be performed on the data. It enables us to think abstractly about the data We can separate concepts from implementation. Typically, we choose a data structure and algorithms that provide an implementation of an ADT. 12

13 ADT Data Methods Simple Example Points Line Shape Length Matrix Vector Advanced Example List Stack Queue Link List Trees 13

14 Point Example Methods Point() Point(int x, int y) Point(Point p) getx() gety() setx() sety() getlength() addx(int x) addy(int y) 14

15 Line Example Attribute 2 Line Methods Line() Line(P1, P2) getlength() getarea() getx() gety() 15

16 Shape Example 16

17 Example Length (feet-inch) Length() Length(Feet, Inch) Add(L1, L2) Subtract(L1, L2) Print () getfrommeter(float Len ) getmeter() 17

18 List

19 Linear List Definitions Linear list is a data object whose instances are of the form (e 1,e 2,,e n ) e i is an element of the list. e 1 is the first element, and e n is the last element. n is the length of the list. When n = 0, it is called an empty list. e 1 comes before e 2, e 2 comes before e 3, and so on. Examples student names order by their alphabets a list of exam scores sorted by descending order 19

20 Implementations of Linear List Array-based (Formula-based) Uses a mathematical formula to determine where (i.e., the memory address) to store each element of a list Linked list (Pointer-based) The elements of a list may be stored in any arbitrary set of locations Each element has an explicit pointer (or link) to the next element Indirect addressing The elements of a list may be stored in any arbitrary set of locations Maintain a table such that the ith table entry tells us where the ith element is stored Simulated pointer Similar to linked representation but integers replace the C++ pointers 20

21 ADT for LinearArrayList class LinearArrayList { Methods Create(): create an empty linear list Create(s): create a list with size s IsEmpty(): return true if empty, false otherwise ISFull(): return true if List is full Length(): return the list size Find(k): return the k th element of the list Search(x): return the position of x in the list Delete(k): delete the k th element and return it Insert(k,x): insert x just after the k th element Print(out): put the list into the output stream out Add(x): Add new item to the list Clear(): clear all items Remove(): Remove top item of the list } 21

22 Array List createlist() insertfirst() insertlast() insertmiddle() isfull() finditems() print() clear() 22

23 Array List Remove Item from list 23

24 Example (Java Code) 24