data structures course 1

7/28/2019 Data structures course 1

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Data Structures

[email protected]
mailto:[email protected]:[email protected]


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Organizational

Course objectives: present main data structures,improve programming.

Final grade = sum of all: 1 p appreciation, 4 p

homework, 2 p - laboratory test, 3 p - problemimplementation, 2 p - final exam

if you have >10 p the final grade is 10, if you have


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Important

Academic honesty: cheating leads to failing classand reporting.

OK/encouraged: speak up in class. Two-way, ratherthan one-way communication. Request: be concise,to the point, respect time spent together in class.

Disclaimer: I can make mistakes/be wrong. Let meknow (in person, email) how I can improve things.


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Further reference material

Introduction to Algorithms, Second Edition by: Thomas H.Cormen, Charles E. Leiserson, Ronald L. Rivest, CliffordStein http://mitpress.mit.edu/algorithms/

Adam Drozdek Data structures and algorithms in C++,third edition, Thomson Course Technology, 2005.

Michael T. Goodrich, Roberto Tamassia, David M. MountData Structures and Algorithms in C++.Second Edition

Gabriel Istrate last year lectures:http://gabrielistrate.weebly.com/pentru-studenti.html

other prefered Data Structures books
http://mitpress.mit.edu/algorithms/http://mitpress.mit.edu/algorithms/


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The plan

Linked Lists. Singly linked lists, Doubly linkedlists. Stacks, queues, dequeues.

Binary Search Trees AVL trees

.

Heaps. Red-black trees. Hash tables. Augmenting Data Structures

.


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Why data structures ?

Data structures: a way to define data types we want.

Many tasks can be specified in terms of input and output.

Input/output: data. Divided into types. Predefined (in C: int,long, short, double, etc), or user defined.

Data types can involve packaging multiple elements of

simpler types. Examples: complex numbers (real,

imaginary), enums.

Performance requirements.

Operations abstracted from requirements.

Frequent operations should be fast.


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Examples

Problem 1

Read a stream of words from an input. Maintainset of words, withfrequencies. Want: quickly test if we have seen a word. Quicklyupdate frequency.

Problem 2

Evaluating postfix arithmetic expressions

Problem 3

Computation of shortest paths from a Weighted Graph.


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Example (operations from requirements)

1 2 3 6 7 4 8 5 10 14 13 11 12...

TCP: basis for much of Internet traffic.

Data requirement: We need to buffera packetthat is out-of order.

We need to pop elements that become in-order.

We need to test emptyness of buffer.

We need to produce first missing element

Operation performance O(1)?.


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What are data structures after all ?

(Abstract) sets ofdata ...

E.g. complex numbers: two floats.

... together with operationsone can perform on the

data ...

E.g. integer + (addition), - (subtraction), (multiplication)

... and performance guarantees.

How to precisely implement operations is not a part ofdata structure specification. Concepts, not code.


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Data types

All DS that share a common structure and expose thesame set of operations.

Predefined data types: array, structures, files.

Scalar data type: ordering relation exists among elements. More complicated, dynamic DS: Lists, circular lists, trees,

hash tables, graphs.

Standard template library (STL): library of container

classes, algorithms, and iterators; provides many of thebasic algorithms and data structures of computer science


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E.g. Standard data types: integers

Available on most hardware. Often subject tostandardization.

Integer data type: subset of integers.

Operations: exact. In case of overflow computationstopped.

Unsigned/signed integers, twos complement.Value Unsigned Signed Two's complement

-128 - - 10000000-127 - 11111111 10000001

-1 - 10000001 11111111

0 00000000 00000000 00000000

127 01111111 01111111 01111111

128 10000000 - -

255 11111111 - -


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Real numbers: data types

floating point representation.

simple (32 bits), double (64 bits), extended precision (80bits ).

representation: three parts. sign, exponent,significand(mantissa).

mantissa: normalized (by adjusting exponent) so that mostsignificant bit is 1.

e.g. double: 64 bits, one for the sign, 52 bits for mantissa(normalized), 11 bits exponent (base 2).

arithmetic operations: +,-,*, /

also % and bitwise operations.


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Array data type/Vector

Ensures random access to its elements.

Composed of objects of the same type.

int myarray[10]; One dimensional arrays.

Multidimensional arrays.

type name[lim1]...[limn];

alternative in C++: vector.


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Example using vectorclass

#include

using namespace std;

int main(){

static const int SIZE = 10000;

vector arr( SIZE );

...

}


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some OOP

OOP: revolves around concept ofobject

Objects: created using class definition

Combining of data and related operations iscalled encapsulation.

Allow us to conceal details of object operationsfrom other objects (information-hiding).


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Classes

class C{

public:

... (functions and data members)

private:

... (functions and data members)

}


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Classes: Constructors/Destructors

class C{

public:

C(); // constructor

C(const C &); // copy constructor

~C(); // destructor

...

}


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Operations: message passing to objects

class person{public:

person(char *s="", int i=0, double d=1.0){strcpy(name,s);age = i;

credit = d;}void memberFunction1(){ ...}void memberFunction2(int i, char *s = "unknown") { }

protected:

char name[20];int age;double credit;

};

C object1("object1", 100,2000), object2("object2"), object3;

object1.memberFunction1();object1.memberFunction2(123);


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Namespaces & Streams

using namespace std;

string a;

cout a;

or

std::cout


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Pointers

Variables that hold addresses of other variables.

int i=15, j, *p, *q;

Dynamic memory allocation:

p = new int; p = (int *)malloc(sizeof(int));

Assignment: *p=20;

Deallocation: delete p; free(p);

Delete reference: upon deallocation should assign p = 0;


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Pointers and arrays

int a[5],*p;

for(sum=a[0],i=1;i


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Pointers and reference variables

int n =5, *p = &n, &r =n;

ris a reference variable. Must be initialized in definitionas reference to a particular variable.

reference: different name for/constant pointer to variable.cout


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Generic Classes/Functions: Motivation

swap two integers

void swapint(int *a, int *b){

int temp = *a;

*a = *b;

*b = temp;

} swap two reals

void swapfloat(float *a, float *b){float temp = *a;

*a = *b;

*b = temp;

}


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Generic Functions

template (genType &el1, genType &el2){

genType tmp = el1;

el1 = el2;

el2 = tmp;

}

more general code

reusing code


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Generic Classes

template class genClass{

genType storage[50];

...

}

template class genClass2{

genType storage[size];

...

}

genClass intObject1;

genClass2 intObject2;

E.g. see map from C++


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Conclusions

some syntaxes of C++

For more details: read, practice!

Any questions?

data structures course 1

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