propedéutico de programación coordinación de ciencias ...pgomez/cursos/programacion/... · how...

Propedéutico de Programación

Coordinación de Ciencias

Computacionales

Semana 4,

Segunda Parte

Dra. Pilar Gómez Gil

http://ccc.inaoep.mx/~pgomez/cursos/programacion/

Versión 1. 24.06.08

Chapter 3 ADT Unsorted List

(continuación)

Tomado de: Dale, N. Weems, C++ Plus Data Structures 4th. Ed. 2007 Instructor material, © Jones & Barlett Publishers

Implementación usando apuntadores

• Se puede construir una lista ligada a través del uso de apuntadores y creación dinámica de espacios para almacenar los elementos conforme van apareciendo.

• Para esto, cada elemento deberá contener información sobre cual es el elemento siguiente de la lista


Representación abstracta de una lista

contenido

Referencia a donde esta el siguiente

contenido

contenido


contenido contenido


contenido

contenido


contenido Lista:

null Tomado de: Dale, N. Weems, C++ Plus Data Structures 4th. Ed. 2007 Instructor material, © Jones & Barlett Publishers

Construcción de listas

• Referencia significa la dirección de memoria donde está almacenado el siguiente elemento. Entonces este campo no contiene realmente un valor, sino una dirección donde se encuentra

• “nulo” significa que esa referencia ya no apunta a nadie mas

• Si una lista esta vacía, entonces vale “nulo”


Linked Implementation



Be sure you

understand the

differences among location,

*location, and location->info


Lo que está pintado de “azul fuerte” es lo que regresa Cada instrucción

Linked Implementation • Private data for the Unsorted List ADT,

linked-list implementation

private: NodeType* listData; int length; NodeType* currentPos; };

List with two items



• How do you know that a linked list is empty?

listData is NULL

• What should the constructor do?

– Set length to 0

– Set listData to NULL

• What about currentPos? We let ResetList take care of initializing

currentPos You write the constructor



• What about the observers IsFull and GetLength?

GetLength just returns length

• Can a linked list ever be full?

Yes, if you run out of memory

Ask for a new node within a try/catch


Linked Implementation bool Unsortedtype::IsFull() const

{

NodeType* location;

try

{

location = new NodeType;

delete location;

return false;

}

catch (std::bad_alloc exception)

{

return true;

}

}

What about MakeEmpty?


Linked Implementation void Unsortedtype::MakeEmpty()

{

NodeType* tempPtr;

while (listData != NULL)

{

tempPtr = listData;

listData = listData->next;

delete tempPr;

}

length = 0;

}

Why can we just set

listData to NULL?


13

void UnsortedType::RetrieveItem( ItemType& item, bool& found )

// Pre: Key member of item is initialized.

// Post: If found, item’s key matches an element’s key in the list

// and a copy of that element has been stored in item; otherwise,

// item is unchanged.

{ bool moreToSearch;

NodeType* location;

location = listData;

found = false ;

moreToSearch = ( location != NULL )

while ( moreToSearch && !found )

{

if ( item == location->info ) // match here

{ found = true;

item = location->info;

}

else // advance pointer

{ location = location->next;

moreToSearch = ( location != NULL );

}

}

}



Linked Implmentation


15


How do we go about building a linked list?

Create a list of one item

Get a node using new

location = new NodeType

Put value into info portion of node

location->info = item

Put pointer to node in external pointer

listData = location


16


We forgot something: We must put NULL in the Next position of the first node



How do we add a node to our list?

Get a node using new

location = new NodeType

Put value into info portion

location->info = Item

Put node into list …

Where? Where should the node go? Does it matter?



Now we must put the two parts together--carefully!


Liked Implementation

These steps

must be done in

this order! Why?


Linked Implementation void UnsortedType::InsertItem ( ItemType item )

// Pre: list is not full and item is not in list.

// Post: item is in the list; length has been

incremented.

{

NodeType* location;

// obtain and fill a node

location = new NodeType;

location->info = item;

location->next = listData;

listData = location;

length++;

}


Linked Implementation How do you delete an item?

Find the item

Remove the item


2 posibilidades: Borrar el primero Borrar uno en- medio

Linked Implementation NodeType* = listData;

NodeTyype* tempLocation;

// Find the item

if (item.ComparedTo(listData->info == EQUAL)

{ // item in first location

tempLocation = location;

listData = listData->next;

}

else

{

while (item.ComparedTo((location->next)->info) != EQUAL)

location = location->next;

tempLocation = location->next;

location->next = (location ->next)->next;

}

delete tempLocation;

location--;

}



• ResetList and GetNextItem

What was currentPos in the array-

based implementation?

What would be the equivalent in a

linked implementation?


Linked Implementation void UnsortedType::ResetList()

{

currentPos = NULL;

}

void UnsortedType::GetNextItem(ItemType& item)

{

if (currentPos == NULL)

currentPos = listData;

else

currentPos = currentPos->next;

item = currentPos->info;

}

Postcondition on GetNextItem has changed: Explain


UML Diagram

Note the

differences between the UML Diagrams

for the two

implementations


Class Destructors

• Recall: listData is deallocated when it goes out of scope but what listData points to is not deallocated

• Class Destructor

• A function that is implicitly called when class object goes out of scope

• ~UnsortedType(); // Destructor


• Ver unsorted.h (implementación ligada)

• Ver unsorted.cpp (implementación ligada)

http://ccc.inaoep.mx/~pgomez/cursos/programacion/presentaciones/l_unsorted.h

http://ccc.inaoep.mx/~pgomez/cursos/programacion/presentaciones/l_unsorted.cpp

propedéutico de programación coordinación de ciencias ...pgomez/cursos/programacion/... · how...

Documents