- DSA using C - Discussion
- DSA using C - Useful Resources
- DSA using C - Quick Guide
- DSA using C - Recursion
- DSA using C - Sorting techniques
- DSA using C - Search techniques
- DSA using C - Graph
- DSA using C - Heap
- DSA using C - Hash Table
- DSA using C - Tree
- DSA using C - Priority Queue
- DSA using C - Queue
- DSA using C - Parsing Expressions
- DSA using C - Stack
- DSA using C - Circular Linked List
- DSA using C - Doubly Linked List
- DSA using C - Linked List
- DSA using C - Array
- DSA using C - Concepts
- DSA using C - Algorithms
- DSA using C - Environment
- DSA using C - Overview
- DSA using C - Home
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DSA using C - Priority Queue
Overview
Priority Queue is more specipzed data structure than Queue. Like ordinary queue, priority queue has same method but with a major difference. In Priority queue items are ordered by key value so that item with the lowest value of key is at front and item with the highest value of key is at rear or vice versa. So we re assigned priority to item based on its key value. Lower the value, higher the priority. Following are the principal methods of a Priority Queue.
Basic Operations
insert / enqueue − add an item to the rear of the queue.
remove / dequeue − remove an item from the front of the queue.
Priority Queue Representation
![Queue](/dsa_using_c/images/queue.jpg)
We re going to implement Queue using array in this article. There is few more operations supported by queue which are following.
Peek − get the element at front of the queue.
isFull − check if queue is full.
isEmpty − check if queue is empty.
Insert / Enqueue Operation
Whenever an element is inserted into queue, priority queue inserts the item according to its order. Here we re assuming that data with high value has low priority.
![Insert Operation](/dsa_using_c/images/queue_insert.jpg)
void insert(int data){ int i =0; if(!isFull()){ // if queue is empty, insert the data if(itemCount == 0){ intArray[itemCount++] = data; } else { // start from the right end of the queue for(i = itemCount - 1; i >= 0; i-- ){ // if data is larger, shift existing item to right end if(data > intArray[i]){ intArray[i+1] = intArray[i]; } else { break; } } // insert the data intArray[i+1] = data; itemCount++; } } }
Remove / Dequeue Operation
Whenever an element is to be removed from queue, queue get the element using item count. Once element is removed. Item count is reduced by one.
![Queue Remove Operation](/dsa_using_c/images/queue_remove.jpg)
int removeData(){ return intArray[--itemCount]; }
Example
#include <stdio.h> #include <string.h> #include <stdpb.h> #include <stdbool.h> #define MAX 6 int intArray[MAX]; int itemCount = 0; int peek(){ return intArray[itemCount - 1]; } bool isEmpty(){ return itemCount == 0; } bool isFull(){ return itemCount == MAX; } int size(){ return itemCount; } void insert(int data){ int i =0; if(!isFull()){ // if queue is empty, insert the data if(itemCount == 0){ intArray[itemCount++] = data; } else { // start from the right end of the queue for(i = itemCount - 1; i >= 0; i-- ){ // if data is larger, shift existing item to right end if(data > intArray[i]){ intArray[i+1] = intArray[i]; } else { break; } } // insert the data intArray[i+1] = data; itemCount++; } } } int removeData(){ return intArray[--itemCount]; } int main() { /* insert 5 items */ insert(3); insert(5); insert(9); insert(1); insert(12); // ------------------ // index : 0 1 2 3 4 // ------------------ // queue : 12 9 5 3 1 insert(15); // --------------------- // index : 0 1 2 3 4 5 // --------------------- // queue : 15 12 9 5 3 1 if(isFull()){ printf("Queue is full! "); } // remove one item int num = removeData(); printf("Element removed: %d ",num); // --------------------- // index : 0 1 2 3 4 // --------------------- // queue : 15 12 9 5 3 // insert more items insert(16); // ---------------------- // index : 0 1 2 3 4 5 // ---------------------- // queue : 16 15 12 9 5 3 // As queue is full, elements will not be inserted. insert(17); insert(18); // ---------------------- // index : 0 1 2 3 4 5 // ---------------------- // queue : 16 15 12 9 5 3 printf("Element at front: %d ",peek()); printf("---------------------- "); printf("index : 5 4 3 2 1 0 "); printf("---------------------- "); printf("Queue: "); while(!isEmpty()){ int n = removeData(); printf("%d ",n); } }
Output
If we compile and run the above program then it would produce following output −
Queue is full! Element removed: 1 Element at front: 3 ---------------------- index : 5 4 3 2 1 0 ---------------------- Queue: 3 5 9 12 15 16Advertisements