Algorithms Question Answers Set1

7/23/2019 Algorithms Question Answers Set1

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PAPER-VII

ALGORITHMS

What is time and space complexity?

Ans:- Time complexitya function which

describes the amount of time an algorithm

akes in terms of the amount of i/p to thealgorithm.

Space complexitya function whichdescribes the amount of memory (space)

an algorithm takes in terms of the amount

of input to the algorithm.

Dijkstra's Algorithm:-The time required

by Dijkstra's algorithm is O(|V|2). It wil

be reduced to O(|E|log|V|) if heap is used


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o keep {v in V\Si: L(v) < infinity}.

Prim's Algorithm:-The time required by

Prim's algorithm is O(|V|2). It will beeduced to O(|E|log|V|) if heap is used to

keep {v in V\Si: L(v) < infinity}.

Kruskal algorithm:- The time requiredby Kruskal's algorithm is O(|E|log|V|).

Travelling Salesman Problem.:-It is a

raditional issue that has to do witmaking the most efficient use of resource

while at the same time expending the leas

amount of energy in that utilization. The

designation for this type of problem hail

back to the days of the travelingsalesman

who often wished to arrange travel in a

manner that allowed for visiting the mos


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owns without having to double back and

cross into any given town more than once

Poission process:-It is a collectio{N(t) : t 0} of random variables

where N(t) is the number of events tha

have occurred up to time t (starting fro

ime 0). The number of events betweeime aand time bis given asN(b) N(a

and has aPoisson distribution

Each realization of the process {N(t)} i

a non-negative integer-valued step

function that is non-decreasing, but fo

ntuitive purposes it is usually easier to

hink of it as a point pattern on [0,) (thepoints in time where an event occurs)

The Poisson process is a continuous-time

process. A Poisson process is a pure

birth process, the simplest example o
http://en.wikipedia.org/wiki/Realization_(probability)http://en.wikipedia.org/wiki/Poisson_distributionhttp://en.wikipedia.org/wiki/Random_variable


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a birth-death process.

Inclusion Principal:- The principle thatfA and B are finite sets, the number o

elements in the union of A and B can be

obtained by adding the number o

elements in A to the number of elementn B, and then subtracting from this sum

s the number of elements in the

ntersection ofAandB.

Propositional Satisfiability Problem:-A

propositional satisfiability problembriefly called SAT, consists of a

formula F 2 L(R), and is the problem to

decide whether F is satisfiable.
http://en.wikipedia.org/wiki/Birth-death_process


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SAT is a combinatorial decisio

problem.

1. Decision variant yes/no

answer .2. Search variant find a model i

F is satisfiable

BFS AND DFS

Breadth-first Search:-

The general idea behinda breadth-first search beginning

at a starting vertex A is as

follows. First we process the


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starting vertex A.Then

we process all the neighbors

of A.Then we process allthe neighbors of neighbors

of AAnd so on. Naturally we

need to keep track of theneighbors of a

vertex, andwe need toguarantee

that no vertex is processed twiceThis is accomplished by using a

QUEUE to hold vertices that arc

waiting to he processed, and bya field STATUS which tells us the

current status


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of a vertex.The algorithm follows

Algorithm (Breadth-first Search):This algorithm executes a breadth-firstsearch on a graph G beginning with astarling vertex A

Step 1. Initialize all vertices to theeady state (STATUS = 1)

Step 2. Put the starting vertex A inQUEUE and change the status of A tohe waiting state (STATUS =2).

Step3. Repeat Steps 4 and 5 untilQUEUE is empty.

Step 4.Remove the front vertex No ofQUEUE. Process N, and set STATUS (N)= 3, the processed state.

Step 5. Examine each neighbor J of N


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a) If STATUS (J)= 1 (ready state), add Jo the rear of QUEUE and reset

STATUS (J) - 2 (waiting state).

b) If STATUS (J) = 2 (waiting state) orSTATUS (J) = 3 (processed state), ignorehe vertex J.

[End of Step 3 loop.]

Step 6.Exit.

Again, the above algorithm will process

only those vertices which are connectedo the starting vertex A.that is,he connected componentncluding A. Suppose

one wants to process all the vertices in

he graph G. Then the algorithm must bemodified so that itbegins again with another vertex (whichwe callB) that is still in the ready stateSTATUS = 1).

This vertex Bain be obtained by


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raversing through thelist of vertices.

EXAMPLESuppose the BFS Algorithm 8.1? B is

applied to the graph in Fig. 8-28. Thevertices are processed in the followingorder:A, D, C, B, F, E, G, HSpecifically, Figure (a)shows thesequence of waiting lists in QUEUE andhe vertices being processedAgain,

each vertex, excluding A,comes froman adjacency list and hence correspond-

to an edge of thegraph. Theseedges form a spanning tree of G whichs pictured in Figure (b).

Again,the numbersindicate theorder the ed

are added to the tree.Observe that this spanning tree isdifferent than the one inFigure (b) which came from a depth-firstsearch


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Depth-first Search:The generaldea behind a depth-first search

beginning at a starting

vertex A is as fellows First weprocess the starting

vertex A. Then we process each

vertex N along with a


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path P which begins at A;that is,

we process a neighbor of A, then

a neighbor of a neighborof A, and so on. After coming to

a "dead end", that is, to a vertex

with no unprocessed neighbor,we backtrack on the path P until

we can continue along another

path P. And so on. Thebacktracking is accomplished by

using a STACK to hold the initia

vertices of future possiblepaths. We also need a field

STATUS which tells us the


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current status of any vertex so

that no vertex is processed more

than once. The algorithmfollows.

Algorithm 1.12A (Depth-first Search):

This algorithm executes a depth-firstsearch on a graph G beginning with astarting vertex A.

Step 1. Initialize all vertices to the

eady state (STATUS = I)

Step 2. Push the startingvertex A onto STACK and change thestatus of A to the waiting state (STATUS= 2).

Step 3. Repeat Steps 4 and 5 untilSTACK is empty.

Step 4. Pop the top vertex N of


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STACK. Process N, and set STATUS (N)= 3; the processed state

Step 5. Examine

each neighbor J of N.

a) If STATUS (J)= 1(ready slate),push Jonto STACK and resetSTATUS (J) = 2 (waiting state).

b) If STATUS (J)= 2(waiting state),delete the previous J from the STACKand push the current J onto STACK

c) If STATUS (J)= 3(processed state),gnore the vertex J.

[End of Step 3 loop.]

Step 6. Exit.

The above algorithm will process onlyhose vertices which are

connected tothe starting vertex

A, thatis. the connected component


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ncluding A. Suppose one wants toprocess all the vertices in thegraph G.Then the algorithm must bemodified so that it begins

again withanother vertex (which wecall B) that isstill in the ready stateSTATE - 1). This vertex B can be

obtained by traversing through the list ofvertices.

EXAMPLESuppose the DFS Algorithm1.12A isapplied to the graph in fig 1-28.

The vertices are processed in thefollowing order:A, B, E, F, C, G, H, D

Specifically, Fig. (a) shows thesequenceof waiting lists in STACK and the

vertices being processed. We have usedhe slash to indicate that a vertexs deleted from the waiting list. Each

vertex, excludingA, comes froman adjacency list and hence

corresponds to an edge


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of thegraph. Theseedges formaspanning trof G which is pictured in Fig. (A). Thenumbers indicate the orderhat the edges arcadded to the

ree, and the dashed lines indicatebacktracking.

SATELLITE

COMMUNICATION


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A Geosynchronous Earth

Orbit (GEO):- This

satellite has an orbita

period that synchronizes

with the Earths speed orotation. So, for an

observer at a fixed location

on Earth, a GEO satellite

will always return to the

same place in the sky aexactly the same time each

day.


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It is also used in the Geo-

Stationary Earth

Orbit(GSO) satellite, it is

a special type of GEO, in

which the satellite is placedin orbit directly above the

Earths equator at a precise

height, so that it maintains

the same position relative to

the Earths surface.

Middle Earth Orbit (MEO):-Thi

satellites have orbits ranging from a few


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hundred miles to a few thousand mile

above the earth's surface, with orbita

periods ranging from around two to 12

hours. MEO is used mainly for satellitenavigation systems such as GPS, Galileo

Glonass and Beidu.

LOW EARTH ORBIT(LEO):-LEO

systems fly about 500 to 1,500 kilometer

above the Earth. Aypical LEO satellite takes less than two

hours to orbit the Earth,

and are only visible for 15 to 20 minute

each pass.Low earth orbiting satellitesare less expensive to launch into orbit as

distance from the earth is less, don't

equire as high signal strength and give


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ess time delay.

Meaning of DPCM Differentia

Pulse Code Modulation- It is amodulation technique invented by the

British Alec Reeves in 1937. It is a

digital representation of an analog signa

where the magnitude of the signal i

sampled regularly at uniform intervals

Every sample is quantized to a series o

symbols in a digital code, which iusually a binary code. PCM is used i

digital telephone systems. It is also the

standard form for digital audio i

computers and various compact discformats. DPCM allows this to be

achieved by describing only the change

between the samples.
http://www.birds-eye.net/definition/p


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ADVANTAGES AND

DISADVANTAGES OF OSI MODEL

Advantages:-1)It provides a standard to

design networking devices by differen

vendors.

2)The protocols in OSI are much hidde

han TCP/IP and can be replaced

elatively easily as the technology

changes.

3) OSI supports both connectionless and

connection-oriented communication in the

network layer

Disadvantages:-1)Due to the complexity

of the system poor performance i


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obtained, especially in some real time

applications.

2) Direct substitution of layers is noalways possible e.g. if a LAN wit

broadcast capability is inserted below a

network protocol that did not support thi

facility, then this service would be lost tohe upper layers.

3) Although protecting equipment fro

becoming obsolete it simultaneouslyhinders technological advancement.

DATA TRANSMISSION

The transmission mode refers to the

number of elementary units of informatio

bits) that can be simultaneously

ranslated by the communications channel


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PARALLEL

CONNECTION:-

Parallel connectio

means simultaneouransmission ofNbits. These bits are sen

simultaneously overNdifferent channels.

SERIALCONNECTION: -In aserial connection, the dataare sent one bit at a time

over the transmission channel. Howeversince most processors process data iparallel, the transmitter needs toransform incoming parallel data into

serial data and the receiver needs to dohe opposite.

Asynchronous data transmission mode:


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n this mode, each character is sent a

rregular intervals in time. So, fo

example, imagine that a single bit i

ransmitted during a long period osilence... the receiver will not be able to

know if this i

00010000,10000000,00000100 . To

emedy this problem, each character i

preceded by some information indicatin

he start of character transmission (the

ransmission start information is calleda START bit) and ends by sending end-of

ransmission information (called STOP

bit, there may even be several STOP

bits).

ADVANTAGES: - 1)It is faster means o

connecting 2) It is Simple. 3) Doesn

equire synchronization of bot


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communication sides. 4)H/W cost is very

cheap.

DISADVANTAGES:-1)It is less reliable2) Large relative overhead. 3) a hig

proportion of the transmitted bits are

uniquely for control purposes and thu

carry no useful information.

Synchronous data transmission mode:

n this mode, the transmitter and receive

are paced by the same clock. The

eceiver continuously receives (eve

when no bits are transmitted) thenformation at the same rate the

ransmitter send it. This is why the

ransmitter and receiver are paced at the

same speed


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ADVANTAGES:- 1) supplementary

nformation is inserted to guarantee tha

here are no errors during transmission.

2) It is highly efficient. 3)Lower

overhead and thus, greater throughput 4

t is more reliable.

5)It is possible to have both sides try to

synchronize the connection at the same

ime.

DISDVANTAGES:- 1)The mai

disadvantage of synchronous transmissio

s recognising the data at the receiver.

2)It is slower than asynchronou

ransmission mode. 3)Hardware is more

expensive 4)Slightly more complex.


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ALOHA

ALOHA is a medium access protocol thawas originally designed for ground based

adio broadcasting however it i

applicable to any system in whic

uncoordinated users are competing for the

use of a shared channel. Pure ALOHA

and slotted ALOHA are the two version

of ALOHA.

Pure ALOHA:- Pure ALOHA uses a

very simple idea that is to let user

ransmit whenever they have data to sendPure ALOHA is featured with the

feedback property that enables it to liste

o the channel and finds out whether the

frame was destroyed. Feedback i
http://www.blurtit.com/q646302.htmlhttp://www.blurtit.com/q328653.html


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mmediate in LANsbut there is a delay o

270 milli sec in the satellitetransmission

t requires acknowledgment if listening to

he channel is not possible due to someeason. It can provide a channe

utilization of 18 percent that is no

appealing but it gives the advantage o

ransmitting any time.

SLOTTED ALOHA:-It divides time

nto discrete intervals and each interval

corresponds to a frame of data. It requires

users to agree on slot boundaries. It does

not allow a system to transmit any time.

nstead the system has to wait for thebeginning if the next slot

Differnce b/w narrowband and

broadband communication
http://www.blurtit.com/q898327.htmlhttp://www.blurtit.com/q898327.html


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channel:-Narrowband is associated with

dial up accounts with your ISP usually up

o speeds of 54kps but can be faster if you

use ISDN connections.

Broadband on the other hand is faster

connections up to 8mb ps and is always

online ie connected to the Internet evenwhen your PC is switched off

PAPER IX


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OPERATING SYSTEM

Internal fragmentation:- It occurs

when storage is allocated withoutntention to use it. This space is

wasted. While this seems foolish, it is

often accepted in return for increased

efficiency or simplicity. The terminternal" refers to the fact that the

unusable storage is inside the

allocated region but is not being used.

t is difficult to reclaim; usually the

best way to remove it is with a design

change.

External fragmentation:- It is the

phenomenon in which free storage

becomes divided into many small

pieces over time. It is a weakness of


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certain storage allocation algorithms,

occurring when an application

allocates and deallocates regions of

storage of varying sizes, theallocation algorithm responds by

eaving the allocated and deallocated

egions interspersed.. The term

external" refers to the fact that the

unusable storage is outside the

allocated regions.

Effects:-1)The most common side

effect of fragmentation is slowdown.

Fragmentation causes slowdown. 2)

A rather more serious side effect iswhat file fragmentation is. File

fragmentation is a direct result of

external fragmentation,occurs during

he process of data removal and


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expansion, another program. 3)

Another effect of fragmentation is the

program to malfunction, i.e function

slowly or do not function at all.

Solution:- The only viable solution to

fragmentation is defragmentation.

Defragmentation runs a

comprehensive scan on the hard drive

and all the files inside of it, and

determines the optimal way to storeour data. Although defragmentation

cannot solve internal fragmentation, it

will completely solve external

fragmentation.

Defragmentation is a process tha

educes the amoun

of fragmentation in file systems. It doe
http://en.wikipedia.org/wiki/File_systemhttp://en.wikipedia.org/wiki/File_system_fragmentation


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his by physically organizing the content

of themass storage device to store files i

a contiguous region if possible, or in the

smallest possible number of regionfragments) if not. It also attempts to

create larger regions of free space usin

compaction to impede the return o

fragmentation.

Q) Why paging is used?

Ans:-Paging is used for faster access

o data. When a program needs a

page, it is available in the main

memory as the OS copies a certain

number of pages from your storage

device to main memory. Paging

allows the physical address space of
http://en.wikipedia.org/wiki/Contiguityhttp://en.wikipedia.org/wiki/Computer_filehttp://en.wikipedia.org/wiki/Mass_storage


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a process to be noncontiguous.

Advantages of Paging:-1) Easy to

allocate physical memory 2)Easy toallocate a frame, just remove it from

ts free list 3) complication for

kernel contiguous physical memory

allocation 4) Easy to page outchunks of programs

Disadvantages of paging:- 1)

Wastage of memory space. 2)Memory reference overhead 3)

Memory required to hold page tables

hat can be large

Complete Cocomo Model:- The main

shortcoming of basic and intermediate

COCOMO model is that they consider a


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software product as a single

homogeneous entity. The system is made

up of sub-systems which have their own

characteristics. Sub-systems may havedifferent inherent development

complexity, reliability requirements may

be high, development team experience.

The complete COCOMO model consider

hese differences in characteristics of the

subsystems and estimates the effort and

development time as the sum of theestimates for the individual subsystems.

Q) What do you mean by S/W quality

assurance?Ans:- Software Quality Assurancenvolves the entire software developmen

PROCESS - monitoring and improvin

he process, making sure that any agreed


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upon standards and procedures arefollowed, and ensuring that problems arefound and dealt with. It is oriented to

prevention'.

TESTING

I) Bottom-up Testing Strategy

1)The subsystem in the lowest layer ofhe call hierarchy are tested individually

2) Then the next subsystems are testedhat call the previously tested subsystems3)This is done repeatedly until alsubsystems are included in the testin

Special program needed to do the testing,II) Top-down Testing Strategy

1) Test the top layer or the controlling

subsystem first 2) Then combine all the


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subsystems that are called by the tested

subsystems and test the resultin

collection of subsystems 3)Do this until

all subsystems are marked into the test4) Special program is needed to do the

esting,

Test stub : A program or a method thasimulates the activity of a missin

subsystem by answering to the callin

sequence of the calling subsystem and

eturning back fake data.

III) Sandwich Testing Strategy

1) It Combines top-down strategy wit

bottom-up strategy 2)The system is view

as having three layers A target layer in the

middle 3)A layer above the target 4) A

ayer below the target 5) Testin


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converges at the target layer

IV) Modified Sandwich Testing

Strategy

1)Middle layer with drivers and stubs 2

Top layer with stubs 3) Bottom laye

with drivers 4) Top layer accessing

middle layer (top layer replaces drivers)5)Bottom accessed by middle layer

V) Big-Bang Strategy:-

Big-Bang approach is very simple in itphilosophy where basically all themodules or builds are constructed andested independently of each other and

when they are finished, they are all puogether at the same time.Advantage of this approach is that it ivery quick as no drivers or stubs are

needed, thus cutting down on the


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Process CPU

Burst

Remainder

CPU time

Remaind

CPU time

P1 20 16 12

P2 5 1 0

P3 6 2 0

P1 P2 P3 P1 P2 P3 P

development time.Disadvantage:- 1) the least effective. 2t is very demanding on the resources 3)

There is really nothing to demonstrateuntil all the modules have been built andntegrated.

Cpu Scheduling( round robin)

Quantum = Q = 4


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0

4

8 12 16 17 19 3

Average waiting time: Waiting Time =

Final Start Time - Previous Time i

CPU - Arrival Time)

(19-8-0)+(16-4)+(17-4)]/3=

11+12+13)/3=12

Every one gets about the same amount o

waiting time.

S/W ENG.

SSADM:- SSADM (Structured System

Analysis & Design Method) is a widely

used computer application developmen


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method in the UK, where its use is ofte

specified as a requirement for governmen

computing projects. It is increasingly

being adopted by the public sector iEurope.

SSADM's objectives are to:

Improve project management &

control

Make more effective use of

experienced and inexperienced

developmentstaff

Develop better quality systems

Make projects resilient to theloss of staff

Enable projects to be supported

by computer-based tools such as

computer-aided software


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engineering systems

Establish a framework for good

communications between

participants in a project

SSADM STEPS:-

SSADM sets out a cascade or waterfall

view of systems development, in which

there are a series of steps, each of

which leads to the next step,

SSADM's steps, or stages, are:Feasibility

Investigation of the current

environment

Business systems optionsDefinition of requirements

Technical system options

Logical design


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Physical design

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