Question

Skills needed to complete this assignment: template metaprogramming.

PROGRAMMING LANGUAGE: C++

PROMPT:

Write a template version of a class PQueue that implements a priority queue. A priority queue is a list of items that is always ordered by priority. Each item that is added to the list requires an associated priority value, an integer for this problem, where 0 represents the highest priority and larger values are lower in priority. Removing an item from the queue removes the item with the highest priority (the smallest priority value).

The class must have the following public functions 1. add: take a generic type as the item to be added and an integer as the priority and adds the item to the priority queue. 2. remove: removes and returns from the priority queue the item that has the highest priority. If multiple items have the same priority, anyone of them could be returned. 3. empty: returns true if the priority queue is empty, and false otherwise. Defining other functions is optional

You can use any standard library classes except the priority_queue. You must submit at least one file: pqueue.h. You can submit other files if they are necessary to compile your class.

Hints: 1. You can start with a basic type like char, then convert to class to a class template. 2. For class templates, you need to have the class definition and its member functions definitions in the same file, or to have all the files (header and implementation) including in the main program. Otherwise the compiler cannot link the files.

INPUT/OUTPUT EXAMPLE

Character queue: Enter how many items you want to add to the queue: 4 Enter item and its priority: A 12 Enter item and its priority: B 1 Enter item and its priority: C 3 Enter item and its priority: D 0 Items in queue in order of priority: D B C A String queue: Enter how many items you want to add to the queue: 3 Enter item and its priority: alpha 3 Enter item and its priority: bravo 1 Enter item and its priority: charlie 2 Items in queue in order of priority: bravo charlie alpha

MAIN.CPP

#include #include #include "pqueue.h" #include "pqueue.cpp" using namespace std;

template void testPQueue(PQueue &pq) { int n; cout << "Enter how many items you want to add to the queue: "; cin >> n; for(int i=0; i { T input; int priority; cout << "Enter item and its priority: "; cin >> input >> priority; p1.add(input, priority); } cout << "Items in queue in order of priority:" << endl; while(!pq.empty()) { cout << pq.remove() << endl; } }

int main() { PQueue pqc; cout << "Character queue:" << endl; testPQueue(pqc); PQueue pqs; cout << "String queue:" << endl; testPQueue(pqs); return 0; }

Answer 1

// pqueue.h

#ifndef PQUEUE_H_
#define PQUEUE_H_

#include <iostream>
#include <vector>
using namespace std;

// structure to represent the elements of the PQueue
template <class T>
struct Item
{
   T value;
   int priority;
};

template <class T>
class PQueue
{
   vector< Item<T> > queue; // queue to store the elements

public:
   void add(T value,int priority);
   T remove();
   bool empty();
};

// function to add the Item with value and priority at the end of queue
template <class T>
void PQueue<T>::add(T value, int priority)
{
   Item<T> item;
   item.value = value;
   item.priority = priority;
   queue.push_back(item);
}

// function to remove and return the value with highest priority i.e lowest priority value
template <class T>
T PQueue<T>::remove()
{
   if(!empty()) // if queue is not empty
   {
       int maxIdx = 0;
       // loop to find the index of the highest priority item
       for(size_t i=1;i<queue.size();i++)
       {
           if(queue[i].priority < queue[maxIdx].priority)
           {
               maxIdx = i;
           }
       }

       T value = queue[maxIdx].value; // get the value of the highest priority item
       queue.erase(queue.begin()+maxIdx); // remove the item

       return value; // return the value
   }

   return T(0);
}

// function to return if the queue is empty or not
template <class T>
bool PQueue<T>::empty()
{
   return queue.size() == 0;
}

#endif

//end of pqueue.h

//main.cpp : C++ program to test PQueue class

#include <iostream>
#include "pqueue.h"
using namespace std;

template <class T>

void testPQueue(PQueue<T> &pq)
{

   int n;

   cout << "Enter how many items you want to add to the queue: ";

   cin >> n;

   for(int i=0; i<n;i++)
   {

       T input;

       int priority;

       cout << "Enter item and its priority: ";

       cin >> input >> priority;

       pq.add(input, priority);

   }

   cout << "Items in queue in order of priority:" << endl;

   while(!pq.empty())
   {
       cout << pq.remove() << endl;
   }

}

int main() {

   PQueue<char> pqc;
   cout << "Character queue:" << endl;
   testPQueue(pqc);
   PQueue<string> pqs;
   cout << "String queue:" << endl;
   testPQueue(pqs);
   return 0;
}

//end of main.cpp

Output: