lecture-2-ds-definitions-2011-1.pdf

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Data structures and algorithms

•

Program design= algorithm + data

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•

Algorithm: is a logical sequence of steps that

describes a complete solution to a given

problem computable in a finite amount of time

problem computable in a finite amount of time.

•

Analysis of algorithms is used to predict the

efficiency of the algorithms in order to select

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the best one.

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Analysis can be done on the:

1

Space (size)

1. Space (size)

2. Time (Speed)

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Data

• Our world is full of DATA that need to be processed, so what is data?

• Data : are nouns of the programming world: the objects that are manipulated, the information that is processed by a computer program.

• Data: The representation of information in a manner suitable for • Data: The representation of information in a manner suitable for

communication or analysis by humans or machines

• In the context of a programming language, the term p g g g g

data

refers to the representation of such information, from the problem domain, by the data types available in the language.

• Data from the computer point of view is just a collection of bits (1,0) • Data from the human beings point of view is numbers, names, lists

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Data abstraction

• Data abstraction: the separation of data type’s

p

yp

logical properties from its implementation.

• Ex. Integers can be physically represented as:

i

d

i

d BCD 2’

l

signed, unsigned, BCD, 2’s complement ….

• But As a programmer, however, you don’t

usually get involved at this level; you simply use

integers. All you need to know is how to declare

an int type variable and what operations are

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Thinking

Thinking…

• In order to use the data in an efficient way we have to answer some questions such as :

questions such as :

• How to store data in a Computer Program? • How to organize the involved Data?

• How data are arranged in relation to each other?How data are arranged in relation to each other? • Which operations and parameters?

• Which data are kept in the memory? • Which are calculated when needed?

• Which are kept in files, and how the files are arranged? • Which method is more efficient?

• Which Programming Language?

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Data Structures

• We need to organize our Data used in a program In data

g

p g

structures

• We need to specify such Data Structures

• Specification of Data Structures can be done through

what called an Abstract Data Types (ADT) that

describes:

• The Types of Data

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Data Structures

• Data type A category of data characterized by the supported elements of the category and the supported operations on those elements

• Atomic or primitive typeAtomic or primitive type A data type whose elements are single none-A data type whose elements are single, none decomposable data items

• In effect, all the Java built-in types are ADTs (Abstract Data Types). A Java programmer can declare variables of those types without understanding the underlying implementation. The programmer can initialize, modify, and

u de y g p e e a o e p og a e ca a e, od y, a d

access the information held by the variables using the provided operations. • Abstract data type: is to define the domain and the structure of the data a

long with a collection of operations that access the data without implementation dependency

• Ex. Integer : N , { +, -,*, / }

Boolean: { true, false} , {and , or, not xor }

• Data structure A collection of data elements whose logical organization reflects a relationship among the elements. A data structure is characterized reflects a relationship among the elements. A data structure is characterized by accessing operations that are used to store and retrieve the individual data elements.

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Data Levels

• In modeling data in a program, we must determine the

abstract properties of the data, choose the

representation of the data, and develop the operations

p

,

p

that encapsulate this arrangement. During this process,

we consider data from three different levels:

•

1.

Logical (or abstract) level:

An abstract view of the data

values (the domain) and the set of operations to

manipulate them. At this level, we define the ADT.

•

2.

Application (or user) level:

A way of modeling real-life

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data in a specific context; also called the problem

domain. Here the application programmer uses the ADT

to solve a problem.

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Aims of studying Data structures

1 analysis and tradeoffs (advantages

1. analysis and tradeoffs (advantages,

disadvantages).

2 time efficiency (organize data so that the

2. time efficiency (organize data so that the

algorithms used to access it are efficient in

time)

time).