Introduction to AlgorithmSession 1

Course : T0974-Algorithm & Object-Oriented Programming IYear : 2011

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Learning Outcome

After taking this course, students should be expected to explain and discuss their own

Algorithms.

Lecture Outline

• Definition of Algorithm• Characteristics of Algorithm• Programming Language• Algorithm Expression• Pseudocode• Flowchart• NS Diagram

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Algorithm Definition

• A precise rule (or set of rules) specifying how to solve some problemwordnetweb.princeton.edu/perl/webwn

• A procedure used to solve a mathematical or computational problem or to address a data processing issue. In the latter sense, an algorithm is a set of step-by-step commands or instructions designed to reach a particular goal. www.colorado.edu/geography/gcraft/gloss/glossary.html

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Example

• Sorting. This algorithm is used to arrange of items or number according of its size.

– Input : a set of positive numbers (a1, a2, a3, …, an)

e.g. 5, 3, 4, 2, 1

– Output: a set of arranged numbers (a’1, a’2, a’3, …, a’n)

e.g. 1, 2, 3, 4, 5• Example of problems which solved using an Algorithm.

– Human Genome Project to identify 100.000 of human DNA genes.

– Search Engines (Yahoo, Google, etc)– GPS Tracking System.

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Characteristics of Algorithm

• Input• Output• Definitness• Finiteness• Effectiveness

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An algorithm should have the following five characteristics :

Programming Language• A sequence of instructions that a computer can

interpret and execute) "the program required several hundred lines of code” --wordnetweb.princeton.edu

• Instruction is a line of code written as part of a computer program –wordnetweb.princeton.edu

• Example :– COBOL (Common Business Oriented Language)– FORTRAN (FORmula TRANslation)– Ada (Ada Lovelace)– C– C++ (C Based Object-Oriented Programming Languange)– Java

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Expressing an Algorithm

Expressing an Algorithm can be expressed using a method below :

• Pseudocode• Flowchart• NS Diagram

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Psedocode

Pseudocode (pronounced SOO-doh-kohd) is a detailed yet readable description of what a computer program or algorithm must do, expressed in a formally-styled natural language rather than in a programming language.—WhatIs.com

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Pseudocode

BEGIN

Hold up the phone

WHILE not dialPress dial

button

WHILE not connected

Waiting dial

IF connected THENWHILE not

finishTalking

Hold down the phone

ENDBina Nusantara University 11

Example of phone calls using pseudocode.

Pseudocode

BEGIN

Number = Input NumberResult = Number % 2

IF Result = 0THEN Print “The number is even

number”ELSE

THEN Print “The number is odd number”

ENDBina Nusantara University 12

Example of Pseudocode to determine odd-even number

Flowchart

• Schematic representation of process or algorithm.

• Schematic is a illustration of system in simplified or symbolic form.

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Flowchart

• Notasi Proses, Data Entry

• Selection :• Flow Lines :• Input/Output:• Stop Notation :

RECTANGLE

DIAMOND

Start

PARALLELOGRAM

CIRCLE

END

Every algorithm process is usually starts from

And ends by

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FlowchartExample of Phone Calling Flowchart

Hold up the phone

Press dial button

Waiting

Start

Dialing

No

Yes

ConnectedNo

Yes

Talking

Finish

No

Yes

Hold down the phone

END

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FlowchartExample of determining odd-even number

Start

Input Number

Number % 2

Print “Odd Number” Print “Even Number”

01

END

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NS Diagram

• NS Diagram is a graphical illustration of structured progamming design.

• Its method is by drawing a table for illustrating an algorithm.

• Founded in 1972 by Isaac Nassi & Ben Shneiderman.

• Known as structograms.

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NS Diagram

• Process notation :

• Selection notation:

• Loop notation :– WHILE

– DO-WHILE

Proses

Kondisi

Betul Salah

Kondisi BelumTerpenuhi

Proses

KondisiBelum Terpenuhi

Proses

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NS Diagram

Example of Phone Calling process using NS Diagram

Hold up the phone

Dialing?

Press dialbutton

Finish?

Talking

Hold down the phone

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NS Diagram

Insert number

Print “EvenNumber”

Number % 2

Equal to 0 Equal to 1

Print “OddNumber”

Example of NS Diagram to determine odd-even numbers

Did you know ?

• The word "algorithm" comes from the name of the ninth-century Persian mathematician Mohammed al-Khowarizmi. He wrote a widely read book entitled Kitab al jabr w'al-muqabala (Rules of Restoration and Reduction) in the year of 825. This book describes many procedures for the manipulation of decimal numbers.

• The word was translated into Latin in the twelve century as “Algoritmi de numero Indorum“ or “Algoritmus on the numbers of the Indians“

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Referensi• Introduction to Algorithms. 2ed. Cormen. 2002. p5-13• Introduction to Java Programming. 8ed. Liang. 2011.

p29-30• Algorithm. http://en.wikipedia.org/wiki/Algorithm• Pseudocode. http://en.wikipedia.org/wiki/Pseudocode• Flowchart. http://en.wikipedia.org/wiki/Flowchart• NS Diagram. http://en.wikipedia.org/wiki/NS_Diagram