DSA Intro

1. Data Structures and Algorithms
An Introduction

2. Course Objectives
 Understanding the concepts of cost and benefits for data
structures
 Understand commonly used data structures
 Understand the effectiveness of data structure
 Select a data structure for specific requirement
 Implement data structures in a programming language

3. Agenda
 Introduction to Data Structures
 Importance and use of Data Structures
 Linked Lists
 Stack
 Queue
 Overview of Trees
 Overview of Graphs
 Sorting Algorithms

4. Session Agenda
 Need of Data Structures
 Data Structures Benefits
 Data Structures Terminologies
 Methodologies for Analyzing Algorithm
 Asymptotic Notations
 Types of Data Structures
 Linear
 Non Linear

5. Session Agenda
 Arrays
 Pointers
 Structures
 Linear Linked Lists
 Singly Linked Lists
 Doubly Linked Lists
 Circular Linked Lists ( Singly and Doubly)

6. Need for Data Structure
 Applications are Complex
 Complex Applications demand more Computations
 Computations require Complex Data
 Complex Data require Complex organization
 Complex Organizations require Complex Processing
(Searching, Insertion, Deletion)
 Data structures organize data
 Provides way of storing data so that it can be used efficiently

7. Selection of Data Structures
 The cost of a solution is the amount of resources
 The choice of data structure and algorithm can make the
difference in execution of a program
 Carefully chosen data structure will allow the most effective
algorithm to be used
 A well-designed data structure allows a variety of critical
operations to be performed, using few resources
 Quality and performance of the final result depends heavily
on choosing the best data structure

8. How to Select a data structure
 Analyze the problem to determine the resource constraints a
solution must meet
 Determine the basic operations that must be supported
 Quantify the resource constraints for each operation
 Select the data structure that best meets these
requirements
 Some questions to ask
 Amount of data to store
 Are all data inserted into the data structure at the beginning,
or are insertions interspersed with other operations?
 Can data be deleted? If so, a more complex representation is
typically required
 Are all data processed in some well-defined order, or is random
access allowed?

9. Data Structure Philosophy
 Each data structure has costs and benefits
 Rarely is one data structure better than another in all
situations.
 A data structure requires:
 space for each data item it stores
 time to perform each basic operation
 programming efforts
 Each problem has constraints on available space and time
 Only after a careful analysis of problem characteristics can
we know the best data structure for the task

10. Methodologies for Analyzing Algorithm
 How much of a computer time and memory is utilized by an
algorithm
 Methodologies
 Empirical Comparison (run programs)
 Asymptotic Algorithm Analysis
 The efficiency analysis concentrates on critical operations:
 data interchanges (swaps)
 comparisons (<, >, ==, ! =)
 arithmetic operations (+, -, =)
 Factors affecting running time
 Critical resources
 Size of the input
 Machine load
 Operating System, Compiler, …
 Problem size

11. Types of Data Structures
 Base Data Structures
 Primitive
 Composite
 Linear Data Structures
 Array
 Linked List
 Non-Linear Data Structures
 Graph
 Tree

12. Arrays
 Arrays are the most common data structure used to store
collections of elements
 Access any element using its index number
 Occupies contiguous memory area
 Example:
int scores[100];
scores[0] = 18;
scores[1] = 5;
scores[2] = 24;
scores
18 5 24 -2134 ... ... ... 14217
Index 0 1 2 3 . . . . . . . 99

13. Pointers
 A variable capable of storing an address is called a pointer
variable.
 Consider the variable declaration:
int *ptr;
 Such a pointer is said to "point to" an integer.
 Storing in ptr the address of an integer variable k is done as
ptr = &k;
 The "dereferencing operator" refers to the value of that
which ptr is pointing to.
*ptr = 7;
 To print to the screen the integer value stored at the address
pointed to by ptr.
printf("%dn",*ptr);

14. Structures
 We can declare the form of a block of data containing
different data types by means of a structure declaration.
 For example,
struct person
{
char name[20];
int age;
float weight;
};
 We now declare a variable of type person
struct person p;
 and access the structure data using this variable as
p.age

15. Structures Continued…
 We can also declare a pointer to a structure with the
declaration:
struct person *ptr;
 and we point it to our example structure with:
st_ptr = &p;
 Now, we can access a given member by de-referencing the
pointer as
(*st_ptr).age = 63;
 Or use an alternative syntax as
st_ptr->age = 63;