05 | 20090224 Algorithm & Efficiency - PowerPoint Presentation

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05 | 20090224 Algorithm & Efficiency

Fazmah Arif Yulianto

CS1013 –

Pengantar

Teknik

Informatika

-

20082

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Slide3

Let’s get serious

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I: Pen and PaperBagaimana kita melakukan

perkalian bilangan?Hafalan

Dengan

Bantuan

Tangan

Kertas

Kalkulator

Manakah

yang

merupakan

Algoritma

?

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Menggunakan Angka Arab 2345 678 x 18760

16415 14070 + 1589910

Mengalikan menggunakan Kertas

Angka Romawi

MMCCCVL

DLXXVIII x

?

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Ciri algoritma:

TerencanaDapat dilakukan

Selesai

Algorithm

Input

Computational steps

Output

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Using natural languageUsing flowchart

Using pseudocodeUsing program source code

…

Specifying an algorithm

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Correctness100%Approx alg

 the error < limitEfficiency:Time & Space efficiency

Simplicity

Generality:

the problem

input range

Algorithm Qualities

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3 Komponen AlgoritmaParadigma IPOSetiap

Algoritma dapat disebutkan:Input : masukan

Proses

: me-

‘*^%$’

-

kan

I

 O

Output :

keluaran

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Latihan I: Pen and PaperPada Algoritma perkalian

menggunakan kertas, sebutkan IPOnya.

Input :

Dua

buah

bilangan

Proses

:

<pre-memory>

Output :

Bilangan hasil perkalian

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II: Resep MasakanResep membuat Cap CayInput : Bahan Masakan, dan Cara MemrosesnyaProses : <interpretasi> <urutan>Output : Cap Cay untuk 6 orang

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Morale IISingkat, ada

Asumsi, Kamus dan atau Knowledge BaseMemungkinkan

Paralel

Processing

Garnish,

Kuah

,

Utama

,

Isi

,

dsb Adanya Konsep ModularityBakso, Maizena, tinggal pake

’ ajaInput – Output - Movement

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The Need of Efficient AlgorithmSuppose that you have an infinitely fast computer equipped with unlimited capacity of free-memory.

Do you still have any reason to study algorithm?

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Absolutely YES!You still have to demonstrate that your solution method terminates and does so with the correct answer

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Back to the real worldComputers may be fast, but they are not infinitely fastMemory may be cheap, but it is not free.

Bounded resources:Computing timeSpace in memory

Energy (mind your laptop battery) etc.

These resources must be used wisely, and efficient algorithms will help you do so

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Performance: the amount of CPU / memory / disk usage / energy etc.Complexity: how well the algorithm scalesBig-Othe number of operations required to perform a function

expression representing some growth relative to the size of the problem (N)Exp: O(1), O(N), O(N2), O(log N), …

Efficiency

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an algorithm takes constant time to run; performance isn’t affected by the size of the problemExp: addressing main memory in a computerarray lookup

O(1)

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the number of operations required to perform a function is directly proportional to the number of items being processedExp: waiting in a line at a supermarketAssume: 2 mins

/ cust (avg)10 cust

 20

mins

; 100

cust

 200

mins

O(N)

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Each member of the group greets every other memberO(N2)

6 persons

 5+4+3+2+1 = 15

7 persons  21

8 persons  28

…

N persons  (N

2

-N)/2 greets

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Big O disregard any constant  (N2-N)as N becomes larger, subtracting N from N2

will have less and less of an overall effectO(N2): (N

2

-N)/2



N

2

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Fast algorithms often make use of very complicated data structures, or use other complicated algorithms as subroutinesChallenge: making more complicated algorithms worthy of consideration in practice

Implementation Complexity

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The world without computer engineers

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Kur

IF 2008

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Let’s do some actions

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Write your algorithm(s) to sort cards from the same suit:You can see all the cards & you can use your both handsCards are all placed face down on the table & you can only use one handWhat is your: average step-count?

Do you find special cases (worst & best)?Card Sorting

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Try to put eight chess queens on an 8×8 chessboard such that none of them is able to capture any other using the standard chess queen's moves8-Queens Puzzle