intro dipti mam

8/6/2019 Intro Dipti Mam

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CO 203

Data Structure

Dipti Rana


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What this subject is about ?

Data structures:

conceptual and concrete ways to organize data forefficient storage and efficient manipulation


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Why do we need them ?

Computers take on more and more complex tasksImagine: index of 8 billion pages ! (Google)

Software implementation and maintenance is difficult

Clean conceptual framework allows for more efficientand more correct code


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Why do we need them ?

Requirements for a good software:Clean Design

Easy maintenanceReliable (no core dumps)

Easy to use

Fast algorithms

Efficient data structuresEfficient algorithms


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Example

A collection of 3,000 texts with avg. of 20lines each, with avg. 10 words / line

600,000 words

Find all occurrences of the word happy

Suppose it takes 1 sec. to check a word for

correct matchingWhat to do?


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Example (contd)

What to do?

Sol. 1 Sequential matching: 1 sec. x 600,000 words = 166 hours

Sol. 2 Binary searching:- order the words

- search only half at a time

Ex. Search 25 in 5 8 12 15 15 17 23 25 27

25 ? 15 15 17 23 25 27

25 ? 23 23 25 27

25 ? 25

How many steps?


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Some example data structures

log2600000 = 19 sec.vs .166 hours!

Set Stack Tree

Data structure = representation and operations

associated with a data type


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What will you learn?

What are some of the common data structures

What are some ways to implement them

How to analyze their efficiency

How to use them to solve practical problems


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Data Structure

PrimitiveData structures that are directly operated upon by machinelevel instructions

int, real, character, pointer, logical data item (true/false)Non Primitive

No direct deletion or insertion operation are performed Arrays [using predefined data types], lists and files


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Data Structure

LinearA list which displays the relationship of adjacency betweenelements is said to be linear

Stack, queue, link listNon Linear

Tree, graphs


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Data Structure

Sequential vs. Non SequentialStatic vs. Dynamic


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Topics

Arrays

Stacks

QueuesLink lists

Trees

GraphsHashing / Dictionaries

Sorting


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What you need

Programming experience

Textbook

Introduction to Data Structures with Applications

Tremblay and Sorenson

C compiler


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Array


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Arrays

Array: a set of pairs (index and value)

data structureFor each index, there is a value associated with

that index.

representation (possible)

implemented by using consecutive memory.


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Arrays in C

int list[5], *plist[5];

list[5]: five integers

list[0], list[1], list[2], list[3], list[4]

*plist[5]: five pointers to integers

plist[0], plist[1], plist[2], plist[3],

plist[4]

implementation of 1-D array

list[0] base address =

list[1] + sizeof(int)

list[2] + 2*sizeof(int)

list[3] + 3*sizeof(int)


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Arrays in C (contd)

Compare int *list1 and int list2[5] in C.

Same: ?

Difference: ?


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Arrays in C (contd)


Same: list1 and list2 arepointers.

Difference: list2 reserves five locations.

Notations:

list2 -

(list2 + i) -

*(list2 + i) -


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Arrays in C (contd)


Same: list1 and list2 arepointers.

Difference: list2 reserves five locations.

Notations:

list2 - a pointer to list2[0]

(list2 + i) - a pointer to list2[i] (&list2[i])

*(list2 + i) - list2[i]


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Address Contents

1228 0

1230 1

1232 2

1234 3

1236 4

Example:

int one[] = {0, 1, 2, 3, 4};

void print1(int *ptr, int rows)

{

printf(Address Contents\n);

for (i=0; i < rows; i++)

printf( ____________________ );

printf(\n);

}

Example :print out address and value


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Address Contents

1228 0

1230 1

1232 2

1234 3

1236 4

Example:

int one[] = {0, 1, 2, 3, 4};

void print1(int *ptr, int rows)

{

printf(Address Contents\n);

for (i=0; i < rows; i++)

printf(%8u%5d\n, ptr+i, *(ptr+i));

printf(\n);

}

Example :print out address and value


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Memory Organization

During run time, variables can be stored inone of three pools

Stack

Static heap

Dynamic heap


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Stack

Maintains memory during function calls

Argument of the function

Local variables

Call Frame

Variables on the stack have limited life time


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Stack - Example

int foo( int a, double f )

{

int b;

}

af

b


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Stack - Example


{

int b;

{

int c;

}

}

af

b


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Stack - Example


{

int b;

{

int c;

}

}

af

b

c


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Stack - Example


{

int b;

{

int c;

}

}

af

b

c


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Stack - Example


{

int b;

{

int c;

}

}

af

b

c


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Stack recursive example

void foo( int depth )

{

int a;if( depth > 1 )

foo( depth-1 );

}

int main()

{

foo(3);

deptha

depth

a

depth

a


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Stack errors?

void foo( int depth )

{

int a;if( depth > 1 )

foo( depth );

}

Will result in run time error:

out of stack space


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Static heap

Memory for global variables

#include

const int ListOfNumbersSize = 1000;

int ListOfNumbers[ListOfNumbersSize];

int main()

{


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Static heap

Variables on the static heap are definedthroughout the execution of the program

Memory on the static heap must be defined atcompile time


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Static heap: reverse example

Example: program to reverse the order of linesof a file

To this task, we need to

read the lines into memory

Print lines in reverse

How do we store the lines in memory?


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const int LineLength = 100;

const int NumberOfLines = 10000;

char Lines[NumberOfLines][LineLength];

int main()

{

int n = ReadLines();

for( n-- ; n >= 0; n-- )

printf(%s\n, Lines[n]);

}


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This solution is problematic:

The program cannot handle files larger than these

specified by the compile time choicesIf we setNumberOfLines to be very large, then theprogram requires this amount of memory even if weare reversing a short file

Want to use memory on as needed basis


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Dynamic Heap

Memory that can be allocated and freed by theprogram during run time

The program controls how much is allocatedand when

Limitations based on run-time situation

Available memory on the computer


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Allocating Memory from Heap

void *malloc( size_t Size );

Returns a pointer to a newmemory block ofsize Size

ReturnsNULL if it cannot allocate memory ofthis size


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Example: strdup

Function to duplicate a string:char *

strdup( char const *p )

{int n = strlen(p);

char* q =(char*)malloc(sizeof(char)*(n+1));

if( q != NULL )

strcpy( q, p );

return q;}

This function is part of the standard library


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Memory Management

void

foo( char const* p )

{

char *q = strdup( p );

// do something with q

}

The allocated memory remains in use

cannot be reused later on

pq

Heap

a

b

\0


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De-allocating memory

void free( void *p );

Returns the memory block pointed byp to thepool of unused memory


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Example of free

void

foo( char const* p )

{

char *q = strdup( p );

// do something with q

free(q);}

This version frees the allocated memory


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Further Knowledge

Read manual page of

malloc

calloc

realloc

free

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