Question

write a java program to Implement a Priority Queue using a linked list. Include a main method demonstrating enqueuing and dequeuing several numbers, printing the list contents for each.

Answer 1

import java.util.* ;

public class Priority_Queue{

// java program to implement Priority_Queue
// using Linked_List

// Node
static class Node {
    int data;
  
    // Lower the values indicates the higher priority
    int priority;
  
     Node next;
  
}

static Node node = new Node();
  
// function to create A New_Node
static Node newNode(int d, int p)
{
    Node temp = new Node();
    temp.data = d;
    temp.priority = p;
    temp.next = null;
  
    return temp;
}
  
// returns the value at head
static int peek(Node head)
{
    return (head).data;
}
  
// function to remove node according to priority

static Node Dequeue(Node head)
{
    Node temp = head;
    (head) = (head).next;
    return head;
}  
  
// function to insert node according to priority
static Node Enqueue(Node head, int d, int p)
{
    Node start = (head);
  
    // Create new Node
    Node temp = newNode(d, p);
  
    // Rare case: The head of list has lesser
    // priority than new node. So insert new
    // node before head node and change head node.
    if ((head).priority > p) {
  
        // insert New_Node before head
        temp.next = head;
        (head) = temp;
    }
    else {
  
        // Traverse the list and find a
        // position to insert new node
        while (start.next != null &&
               start.next.priority < p) {
            start = start.next;
        }
  
        // Either at the ends of the list
        // or at required position
        temp.next = start.next;
        start.next = temp;
    }
    return head;
}
  
// Function to check is list is empty
static int isEmpty(Node head)
{
    return ((head) == null)?1:0;
}
    //Main Function
    public static void main(String []args){
    Node pq = newNode(4, 1);
    // Enqueue operations
    pq =Enqueue(pq, 5, 2);
    pq =Enqueue(pq, 6, 3);
    pq =Enqueue(pq,23424,5);
    pq =Enqueue(pq, 7, 0);
  
    // functions dequeue's the priority_queue until its empty
    while (isEmpty(pq)==0) {
        System.out.printf("%d ", peek(pq));
        //Dequeue operations
        pq=Dequeue(pq);
    }     
    }

}

---------summary--------

what does main function do?

1.Creates a new node first for priority queue .

2.Performs some Enqueue operations.

3.Dequeue's the Priority queue until it's empty.

4.Print's the value of highest priority while dequeueing the queue.