;

bag.clear();

cout << “”isEmpty: returns “” << bag.isEmpty()

<< “”; should be 1 (true)”” << endl;

} // end bagTester

int main()

{

DLinkedBag bag;

cout << “”Testing the Link-Based Bag:”” << endl;

cout << “”The initial bag is empty.”” << endl;

bagTester(bag);

cout << “”All done!”” << endl;

return 0;

} // end main

In a doubly linked list, each node can point to the previous node as well as to the next node. Figure 4-10 shows a doubly linked list and its head pointer. Define a class DoublyLinkedBag using C++ that implements the ADT bag by using a doubly linked list as shown in Figure 4-10.

[Hint: you need to define a class to represent a node in a doubly linked list by modifying the node class we used for linked base implementation of ADT Bag]

Requirement:

+ Create the header DLinkedBag.h to implemented ADT Bag.

+ Use the following program to test your ADT Bag implemented by doubly linked list.

// This program tests the ADT Bag class which is implemented by a doubly

// linked list.

#include

#include

#include “DLinkedBag.h” //doubly linked list bag

using namespace std;

void displayBag(const DLinkedBag& bag)

{

cout << “The bag contains ” << bag.getCurrentSize()

<< ” items:” << endl;

vector bagItems = bag.toVector();

int numberOfEntries = (int)bagItems.size();

for (int i = 0; i < numberOfEntries; i++)

{

cout << bagItems[i] << ” “;

} // end for

cout << endl << endl;

} // end displayBag

void bagTester(DLinkedBag& bag)

{

cout << “isEmpty: returns ” << bag.isEmpty()

<< “; should be 1 (true)” << endl;

displayBag(bag);

string items[] = { “one”, “two”, “three”, “four”, “five”, “one” };

cout << “Add 6 items to the bag: ” << endl;

for (int i = 0; i < 6; i++)

{

bag.add(items[i]);

} // end for

displayBag(bag);

cout << “isEmpty: returns ” << bag.isEmpty()

<< “; should be 0 (false)” << endl;

cout << “getCurrentSize: returns ” << bag.getCurrentSize()

<< “; should be 6” << endl;

cout << “Try to add another entry: add(“extra””) returns “”

<< bag.add(“”extra””) << endl;

cout << “”contains(“”three””): returns “” << bag.contains(“”three””)

<< “”; should be 1 (true)”” << endl;

cout << “”contains(“”ten””): returns “” << bag.contains(“”ten””)

<< “”; should be 0 (false)”” << endl;

cout << “”getFrequencyOf(“”one””): returns “”

<< bag.getFrequencyOf(“”one””) << “” should be 2″” << endl;

cout << “”remove(“”one””): returns “” << bag.remove(“”one””)

<< “”; should be 1 (true)”” << endl;

cout << “”getFrequencyOf(“”one””): returns “”

<< bag.getFrequencyOf(“”one””) << “” should be 1″” << endl;

cout << “”remove(“”one””): returns “” << bag.remove(“”one””)

<< “”; should be 1 (true)”” << endl;

cout << “”remove(“”one””): returns “” << bag.remove(“”one””)

<< “”; should be 0 (false)”” << endl;

cout << endl;

displayBag(bag);

cout << “”After clearing the bag