ascendingpriorityqueue Algorithm
The ascending priority queue algorithm is a data structure that stores elements in a sorted order based on their priority values, with the lowest priority value at the beginning and the highest priority value at the end. Essentially, this algorithm ensures that the element with the lowest priority is always at the front of the queue, making it easy to retrieve and remove when needed. The ascending priority queue can be implemented using various data structures such as arrays, linked lists, or heaps, each offering different trade-offs in terms of time and space complexity.
The primary operations in the ascending priority queue algorithm are insertion, retrieval, and deletion of elements. When inserting an element, the algorithm compares the priority of the new element with the existing elements and finds the appropriate position in the queue to maintain the sorted order. This can be done using various techniques like linear search, binary search, or bubble sort, depending on the underlying data structure. Once the correct position is found, the new element is inserted, and the remaining elements are shifted accordingly. To retrieve the lowest priority element, the algorithm simply returns the first element in the queue, as it is guaranteed to have the lowest priority. Deletion involves removing the first element from the queue and shifting the remaining elements to fill the gap. Depending on the implementation, additional operations such as updating the priority of an element, checking if the queue is empty, or finding the size of the queue may also be supported.
/* Ascending priority queue using Linked List - Program to implement Ascending priority queue using Linked List */
/*A priority queue is a special type of queue in which each element is associated with a priority and is served according
to its priority. If elements with the same priority occur, they are served according to their order in the queue.
Generally, the value of the element itself is considered for assigning the priority.
For example: The element with the highest value is considered as the highest priority element. However, in other cases,
we can assume the element with the lowest value as the highest priority element. In other cases,
we can set priorities according to our needs.
In a queue, the first-in-first-out rule is implemented whereas, in a priority queue, the values are removed on the basis of priority.
The element with the highest priority is removed first.
insert() - Would insert an element in a queue
delete() - Would delete the smallest element in the queue
*/
#include <stdio.h>
#include <stdlib.h>
#define NULL ((void*)0)
struct node
{
int data ;
struct node *next ;
} ;
struct node *front , *rear ;
/* This function initializes the queue to empty by making both front and rear as NULL */
void createqueue()
{
front=rear=NULL ;
}
int empty()
{
if(front==NULL)
return 1 ;
else
return 0 ;
}
void insert(int x)
{
struct node *pnode ;
pnode=(struct node*)malloc(sizeof(struct node)) ;
if(pnode==NULL)
{
printf("Memory overflow. Unable to insert.\n") ;
exit(1) ;
}
pnode->data=x ;
pnode->next=NULL; /* New node is always last node */
if(empty())
front=rear=pnode ;
else
{
rear->next=pnode ;
rear=pnode ;
}
}
int removes()
{
int min ;
struct node *follow , *follow1 , *p , *p1 ;
if(empty())
{
printf("\nQueue Underflow. Unable to remove.") ;
exit(1) ;
}
/* finding the node with minimum value in the APQ.*/
p=p1=front ;
follow=follow1=NULL ;
min=front->data ;
while(p!=NULL)
{
if(p->data<min)
{
min=p->data ;
follow1=follow ;
p1=p ;
}
follow=p ;
p=p->next ;
}
/* Deleting the node with min value */
if(p1==front) /* deleting first node.*/
{
front=front->next ;
if(front==NULL) /* Deleting the only one node */
rear=NULL ;
}
else if(p1==rear) /* Deleting last node */
{
rear=follow1 ;
rear->next=NULL ;
}
else /* deleting any other node.*/
follow1->next=p1->next ;
free(p1) ;
return min ; /* DONT FORGET LAST 2 STATEMENTS.*/
}
void show()
{
struct node *p ;
if(empty())
printf("Queue empty. No data to display \n") ;
else
{
printf("Queue from front to rear is as shown: \n") ;
p=front ;
while(p!=NULL)
{
printf("%d ",p->data) ;
p=p->next ;
}
printf("\n") ;
}
}
void destroyqueue()
{
front=rear=NULL ;
}
int main()
{
int x , ch ;
createqueue() ;
do
{
printf("\n\n Menu: \n") ;
printf("1:Insert \n") ;
printf("2:Remove \n") ;
printf("3:exit \n") ;
printf("Enter your choice: ") ;
scanf("%d",&ch) ;
switch(ch)
{
case 1:
printf("Enter element to be inserted: ") ;
scanf("%d",&x) ;
insert(x) ;
show() ;
break ;
case 2:
x=removes() ;
printf("Element removed is: %d\n",x) ;
show() ;
break ;
case 3:
break ;
}
}
while(ch!=3) ;
destroyqueue() ;
return 0;
}
/* Output of the Program*/
/*
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 12
Queue from front to rear is as shown:
12
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 1
Queue from front to rear is as shown:
12 1
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 14
Queue from front to rear is as shown:
12 1 14
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 3
Queue from front to rear is as shown:
12 1 14 3
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 5
Queue from front to rear is as shown:
12 1 14 3 5
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 1
Queue from front to rear is as shown:
12 14 3 5
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 3
Queue from front to rear is as shown:
12 14 5
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 5
Queue from front to rear is as shown:
12 14
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 12
Queue from front to rear is as shown:
14
Menu:
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 14
Queue empty. No data to display
*/
