Priority Queue Program in C++

This C++ Program demonstrates the implementation of Priority Queue.

Here is source code of the C++ Program to demonstrate the implementation of Priority Queue. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
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 * C++ Program to Implement Priority Queue

```
 */
```
```
#include <iostream>
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```
#include <cstdio>
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```
#include <cstring>
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```
#include <cstdlib>
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```
using namespace std;
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```
 
```
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/*
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 * Node Declaration
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 */
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struct node
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{
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	int priority;
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	int info;
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	struct node *link;
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};
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/*
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 * Class Priority Queue
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 */
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class Priority_Queue
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{
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    private:
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        node *front;
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    public:
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        Priority_Queue()
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        {
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            front = NULL;
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        }
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        /*
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         * Insert into Priority Queue
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```
         */
```

        void insert(int item, int priority)

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        {
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            node *tmp, *q;
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            tmp = new node;
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            tmp->info = item;
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            tmp->priority = priority;
```

            if (front == NULL || priority < front->priority)

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            {
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                tmp->link = front;
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                front = tmp;
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            }
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            else
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```
            {
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                q = front;
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                while (q->link != NULL && q->link->priority <= priority)

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                    q=q->link;
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                tmp->link = q->link;
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                q->link = tmp;
```
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            }
```
```
        }
```
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        /*
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         * Delete from Priority Queue
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         */
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        void del()
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        {
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            node *tmp;
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            if(front == NULL)
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                cout<<"Queue Underflow\n";

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            else
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            {
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                tmp = front;
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                cout<<"Deleted item is: "<<tmp->info<<endl;

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                front = front->link;
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                free(tmp);
```
```
            }
```
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        }
```
```
        /*
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         * Print Priority Queue
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```
         */
```
```
        void display()
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```
        {
```
```
            node *ptr;
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            ptr = front;
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            if (front == NULL)
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                cout<<"Queue is empty\n";

```
            else
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            {	cout<<"Queue is :\n";
```

                cout<<"Priority       Item\n";

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                while(ptr != NULL)
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                {
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                    cout<<ptr->priority<<"                 "<<ptr->info<<endl;

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                    ptr = ptr->link;
```
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                }
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            }
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```
        }
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};
```
```
/*
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 * Main
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```
 */
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```
int main()
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{
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    int choice, item, priority;
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    Priority_Queue pq; 
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    do
```
```
    {
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        cout<<"1.Insert\n";
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        cout<<"2.Delete\n";
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        cout<<"3.Display\n";
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        cout<<"4.Quit\n";
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        cout<<"Enter your choice : "; 
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        cin>>choice;
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        switch(choice)
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        {
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        case 1:
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            cout<<"Input the item value to be added in the queue : ";

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            cin>>item;
```

            cout<<"Enter its priority : ";

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            cin>>priority;
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            pq.insert(item, priority);
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            break;
```
```
        case 2:
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            pq.del();
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            break;
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        case 3:
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            pq.display();
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            break;
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        case 4:
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            break;
```
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        default :
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```
            cout<<"Wrong choice\n";
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```
        }
```
```
    }
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```
    while(choice != 4);
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```
    return 0;
```
```
}
```

$ g++ priority_queue.cpp
$ a.out
 
4.Quit
Enter your choice : 1
Input the item value to be added in the queue : 4
Enter its priority : 2
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 1
Input the item value to be added in the queue : 3
Enter its priority : 3
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 1
Input the item value to be added in the queue : 2
Enter its priority : 4
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 1
Input the item value to be added in the queue : 1
Enter its priority : 5
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 3
Queue is :
Priority       Item
1                 5
2                 4
3                 3
4                 2
5                 1
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 2
Deleted item is: 5
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 3
Queue is :
Priority       Item
2                 4
3                 3
4                 2
5                 1
1.Insert
2.Delete
3.Display
4.Quit
Enter your choice : 4
 
------------------
(program exited with code: 1)
Press return to continue