lecture 3 - queues)

8/7/2019 Lecture 3 - Queues)

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ADT's and C++:ADT's and C++:A ReviewA Review


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ADT's, a reviewADT's, a review

We've learned that it is often necessary toWe've learned that it is often necessary to

develop new data types for our programming,develop new data types for our programming,

and we develop ADT's.and we develop ADT's. In C++, an ADT is constructed using theIn C++, an ADT is constructed using the

classclass construct.construct.

Classes containClasses contain publicpublic andand privateprivate

information, and can have sections so labeled.information, and can have sections so labeled.


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TheThe publicpublic section contains the interface tosection contains the interface tothe ADT. It consists of a set of functionsthe ADT. It consists of a set of functionscalled methods.called methods.

Two special types of methods exist and shouldTwo special types of methods exist and shouldalways be declared:always be declared: constructorsconstructors andanddestructorsdestructors..

Other methods provide the basic ability toOther methods provide the basic ability toexamine and manipulate objects of the newexamine and manipulate objects of the newAbstract Data Type.Abstract Data Type.


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TheThe privateprivate section contains the basis for thesection contains the basis for the

implementation the ADT. It usually containsimplementation the ADT. It usually contains

variables, constants and structures necessary forvariables, constants and structures necessary forthe implementation.the implementation.

This private information is only visible to andThis private information is only visible to and

accessible by the ADT itself; applications usingaccessible by the ADT itself; applications using

the ADT can't see this information or refer to itthe ADT can't see this information or refer to it

in any way.in any way.


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The class definition is placed in a header fileThe class definition is placed in a header filewhich we call the ADT definition header.which we call the ADT definition header.

The ADT definition header should be includedThe ADT definition header should be includedby any source or header file that needs to use theby any source or header file that needs to use theADT in question.ADT in question.

The ADT definition header should also beThe ADT definition header should also be

included by the ADT definition source file,included by the ADT definition source file,which implements all of the methods of thewhich implements all of the methods of theADT.ADT.


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When creating a project that uses the ADT, theWhen creating a project that uses the ADT, the

ADT definition header should be placed in theADT definition header should be placed in the

list of project header files. The ADT definitionlist of project header files. The ADT definitionsource file should be placed in the list of projectsource file should be placed in the list of project

source files.source files.


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Putting all of this together, we arrive at thePutting all of this together, we arrive at the

following two files: IntStack.h and IntStack.cpp.following two files: IntStack.h and IntStack.cpp.


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ADT's, a reviewADT's, a review// FILE: INTSTACK.H Stack of ints ADT definition

#ifndef _INTSTACK#define _INTSTACK

class IntStack{

public:IntStack();~IntStack();bool is_empty()const;bool is_full()const;bool push(const int &value);bool pop(int &value);

bool pop();int top()const;private:

static const int MAX_SIZE = 10000;int top_index;int stack[MAX_SIZE];

};

#endif


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// FILE: INTSTACK.CPP Stack of ints ADT implementation#include "IntStack.h"

IntStack::IntStack(){

top_index = -1;}

IntStack::~IntStack(){

}

boolIntStack::is_empty()const

{return (top_index == -1);

}

bool IntStack::is_full()const{

return (top_index == MAX_SIZE-1);}


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ADT's, a reviewADT's, a reviewbool IntStack::push(const int &value){

bool result = false;if (top_index < MAX_SIZE - 1){

top_index++;stack[top_index]=value;result = true;

}return result;

}

bool IntStack::pop()

{ bool result = false;if (top_index != -1){

top_index--;result = true;

}

return result;}


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ADT's, a reviewADT's, a reviewbool IntStack::pop(int &value){

bool result = false;if (top_index != -1){

value = stack[top_index];top_index--;result = true;

}

return result;

}

int IntStack::top()const{

return stack[top_index];}


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Introducing TemplatesIntroducing TemplatesLast week we created theLast week we created the IntStackIntStack

ADT.ADT.Now, let's generalize it.Now, let's generalize it.


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When using an ADT, the application refers onlyWhen using an ADT, the application refers only

to the declaration of ADT objects and the use ofto the declaration of ADT objects and the use of

the public methods on those objects. Thethe public methods on those objects. The

private information can not be accessed.private information can not be accessed.

You already know how this is done, since youYou already know how this is done, since you

did your homework exercise for the week.did your homework exercise for the week.


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TemplatesTemplates

The problem with the ADT just developed is that it isThe problem with the ADT just developed is that it isonly good for stacks of integers. If we wanted a stackonly good for stacks of integers. If we wanted a stackof student records, or a stack of floats, we're just out ofof student records, or a stack of floats, we're just out of

luck.luck.

We would have to develop a separate ADT for eachWe would have to develop a separate ADT for eachnewnew base typebase type. What a nuisance.. What a nuisance.

Note that each new stack ADT would be basicallyNote that each new stack ADT would be basicallyidentical to the one we just saw, because a stack is aidentical to the one we just saw, because a stack is astack!!!!stack!!!!


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TemplatesTemplates

To get around this, we will redefine the stack asTo get around this, we will redefine the stack asa template ADT.a template ADT.

A template ADT is like a regular ADT, exceptA template ADT is like a regular ADT, exceptthat the base type (or other similar information)that the base type (or other similar information)becomes a parameter of the template.becomes a parameter of the template.

But because of limitations of the C++ language,But because of limitations of the C++ language,

we have to make some adjustments to howwe have to make some adjustments to howthings are put together.things are put together.


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TemplatesTemplates

Each item that appears in the originalEach item that appears in the original .h.h andand.cpp.cpp file is given a template header.file is given a template header.

The class definition is given a template header.The class definition is given a template header.

Each method implementation is given aEach method implementation is given atemplate header.template header.

Template header:Template header:

templatetemplate


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TemplatesTemplatestemplatetemplate

class Stackclass Stack{

public:Stack();~Stack();

bool is_empty()const;bool is_full()const;bool push(const BaseType&value);bool pop(BaseType&value);bool pop();Base

Type

top()

co

nst;

private:static const int MAX_SIZE = 10000;int top_index;BaseTypestack[MAX_SIZE];

};

Template header: BaseType is a

parameter of the template

header,

noteindent

ation

See how the BaseType is now a

parameter


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TemplatesTemplates

A similar thing is done with each method.A similar thing is done with each method.These method template definitions appear in theThese method template definitions appear in theheader file (unfortunately) because C++ can't doheader file (unfortunately) because C++ can't do

it any other way.it any other way. For example, here's push:For example, here's push:


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TemplatesTemplatestemplatetemplate

bool Stack::push(const BaseType&value){


top_index++;stack[top_index]=value;result = true;

}

return result;

}

We do this for each of the methods and arriveat a file that looks like the following:


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TemplatesTemplates// FILE: STACK.H// FILE: STACK.H ADT template definition forstacksADT template definition forstacks

#ifndef _STACK_TEMPLATE#ifndef _STACK_TEMPLATE#define _STACK_TEMPLATE#define _STACK_TEMPLATE

templatetemplate class Stackclass Stack

{ public:Stack();~Stack();bool is_empty()const;bool is_full()const;bool push(const BaseType&value);

bool pop(BaseType&value);bool pop();BaseTypetop()const;

private:static const int MAX_SIZE = 10000;int top_index;BaseTypestack[MAX_SIZE];

};


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TemplatesTemplatestemplate

boolStack::is_empty()const{

return (top_index == -1);}

template bool Stack::is_full()const{

retur

n (top_index == MAX_SIZE-1);}

Notice how in the member specifier we now show the ADT

name with the parameter BaseType in angle brackets.


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bool Stack::push(constBaseType&value)

{


top_index++;stack[top_index]=value;

result = true;}

return result;

}


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bool Stack::pop(BaseType&value){

bool result = false;if

(top_

ind

ex!= -1

)

{

value = stack[top_index];top_index--;result = true;

}return result;

}


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TemplatesTemplates

template BaseType Stack::top()const{

return stack[top_index];}

#endif


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Using TemplatesUsing Templates

Let's look at how we can use a template in anLet's look at how we can use a template in anapplication.application.

The example that follows is for demonstrationThe example that follows is for demonstrationof syntax only.of syntax only.

You would put the source file that follows intoYou would put the source file that follows intoyour projects list of source files and stack.h intoyour projects list of source files and stack.h intoyour list of header files.your list of header files.


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Using TemplatesUsing Templates// Samplesource fileusingthe Stacktemplate ADT#include using namespace std;#include "stack.h"

int main()

{Stacks;int value;

while (cin>>value){

if (value>0)cout


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HomeworkHomework

Write a C++ program that reads a series ofWrite a C++ program that reads a series ofintegers from cin and determines whether it is aintegers from cin and determines whether it is azerozero--marked palindromemarked palindrome..

AA zerozero--marked palindromemarked palindrome consists of a seriesconsists of a seriesof integer values, only one of which has theof integer values, only one of which has thevalue zero. If the values are the same, lookingvalue zero. If the values are the same, lookingbackwards and forwards, with a zero in thebackwards and forwards, with a zero in the

middle, the input is a zeromiddle, the input is a zero--marked palindrome.marked palindrome. For example: 5 10 40 20 0 20 40 10 5 is a zeroFor example: 5 10 40 20 0 20 40 10 5 is a zero--

marked palindrome.marked palindrome.

Use the template ADT inUse the template ADT in stack.hstack.h to do theto do the

checking.checking.


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QueuesQueues

A queue isA queue is homogeneoushomogeneous,, firstfirst--in,in, firstfirst--outout(FIFO)(FIFO)

structure.structure.

HomogeneousHomogeneous means that all the values stored in ameans that all the values stored in a

queue are of the same typequeue are of the same type

FirstFirst--in,in, firstfirst--outoutmeans that the first value insertedmeans that the first value inserted

into the queue would be the first one we would beinto the queue would be the first one we would be

able to extractable to extract

We insert new values at theWe insert new values at the tailtailof the queue andof the queue and

remove values from theremove values from the headheadof the queue.of the queue.


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QueuesQueues

AnAn emptyempty queue is one that contains no values.queue is one that contains no values.We cannot remove from an empty queue.We cannot remove from an empty queue.

In some implementations, it is necessary toIn some implementations, it is necessary to

define adefine a fullfullqueue as one that has no morequeue as one that has no moreroom for any more values. We cannot insertroom for any more values. We cannot insertinto a full queue.into a full queue.

TheThecurrentcurrentvalue in a queue is the first of thevalue in a queue is the first of thevalues in the queue that we inserted.values in the queue that we inserted.


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QueuesQueues

template class Queue

{

public:Queue();

~Queue();

bool is_empty()const;bool is_full()const;bool insert(const Type&value);bool remove(Type &value);

bool remove();Typecurrent()const;// valueathead

// of queuefriend ostream&operator


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friendfriend functionsfunctions

Introducing friendfunctions

Sometimes we have functions that are not actual

methods that we would like to define for a class. For

example, suppose we want to overload the operator


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But


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For example, suppose we decided (incorrectly) that we

would like to supply a friend function that returns the

size of a queue.

Let's call it size_of

friendint size_of (Queue)

Usage: count = size_of(q);


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operator overloadingoperator overloading

We also introduce the concept of operator overloading.

It's like function overloading, but we redefine a C++

operator instead.

We can re-define any existing C++ operator to work on

new kinds of objects. Merely declare:

MyType&operator +(const MyType&operand)

instead of

MyType&add_operand(const MyType&operand)


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operator overloadingoperator overloading

and call bymy_number = x+y;

instead of

my_number = x.add_operand(y);


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QueuesQueues

As with stacks, there are many ways toAs with stacks, there are many ways to

implement a queue: e.g.implement a queue: e.g. -- arrays, Vectors,arrays, Vectors,

linked lists.linked lists.

Array implementation: the traveling problem.Array implementation: the traveling problem.

Unlike stacks, which have one movable endUnlike stacks, which have one movable end

(the top), queues have two movable ends (the(the top), queues have two movable ends (the

head and the tail)head and the tail)


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Array implementation ofQueuesArray implementation ofQueues

private:static const int MAX_SIZE = 100;int head,tail;int size;

Type queue[MAX_SIZE];

}

We maintain a size this time, for convenience (as we will see later)

Insertion is done by: tail++; queue[tail] = value;

removal is done by: value = queue[head];head++;

What happens when we alternately insert and remove?


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0

1

2

3

n-4

n-3

n-2

n-1

head

tail


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This is known asThis is known as driftdrift. The head and tail have. The head and tail havea tendency to move down the array and taila tendency to move down the array and tailreaches the end of the array, not allowing anyreaches the end of the array, not allowing any

more insertions even though theres room inmore insertions even though theres room inthe area before the head.the area before the head.

Solution:Solution: Circular storageCircular storage. Imagine that the. Imagine that thetwo ends of the array are wrapped around sotwo ends of the array are wrapped around sothey meet. The next location after the lastthey meet. The next location after the lastone is the first one!!!one is the first one!!!


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Circular StorageCircular Storage

0

1

n-1

2

3

4

n-2


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Array implementation ofQueuesArray implementation ofQueuestemplate

Queue::Queue(){

size = 0;head = 0;tail = -1;

}

template Queue::~Queue(){

}


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bool Queue::is_empty()const{

return size == 0;}

template boolQueue::is_full()const{

return size == MAX_SIZE;}


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bool Queue::insert(const Type&value){

bool success = !is_full();

if (success)

{size++;

tail = (tail+ 1) % MAX_SIZE;queue[tail] = value;

}

return success;

}


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bool Queue::remove(Type&value){

bool success = !is_empty();

if (success)

{size--;value = queue[head];head = (head+ 1) % MAX_SIZE;

}

return success;

}


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bool Queue::remove(){

bool success = !is_empty();

if (success)

{ size--;head = (head+ 1) % MAX_SIZE;

}

return success;

}


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BaseTypeQueue::current()const{

return queue[head];}


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HomeworkHomework

Write a C++ program that reads a series ofWrite a C++ program that reads a series ofnumbers fromnumbers from cincin. Upon completion, write. Upon completion, write

the nonthe non--negative values tonegative values to coutcout in the reversein the reverse

order from how they came in. Then write theorder from how they came in. Then write the

negative values in the same order as they camenegative values in the same order as they came

in.in.

lecture 3 - queues)

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