C Program to Implement Priority Queue

Priority queue is an abstract data type(ADT) in the computer science which is designed to the operate much like the regular queue except that each element has the certain priority. The priority can determines the order in which elements are dequeued - elements with the higher priority are removed from queue before those with lower priority. It can makes the priority queues an essential tool in the scenarios where the some tasks inherently take the precedence over others.

In this article, we will implement the priority queue using C program.

Representation of Priority Queue in C

Priority queues can typically implemented using the data structures that can efficiently support the required operations - most commonly binary heaps. The binary heap is the complete binary tree where the each node is smaller than its children (min-heap) or larger than its children (max-heap). It can ensuring the retrieval of the node with the highest or the lowest value.

In C, priority queues can also be implemented using the various data structures and it can including the binary heaps, balanced trees or arrays. However, the binary heap can be the most common due to its efficiency. In C programming, the priority queue is implemented as the array where array elements represent the tree nodes.

typedef struct {
 int items[MAX];
 int size;
} PriorityQueue;

Basic Operations of the Priority Queue in C

1. Enqueue Operation

This operation can be used to add the new element to the priority queue with the given priority.

Algorithm

• Add the element to end of the heap.
• Restore the heap property by the comparing the added element with its parent. If it can violates the heap property, swap them.
• Continues this process up the heap until the correct position is found or root is reached.

2. Dequeue (Extract - Min/Max)

This operation can be used to removes and return the elements with the highest max in the max-heap and min in the min-heap of the priority queue.

Algorithms

1. Replace the root of heap with the last element in the heap.
2. Reduce the size of the heap by the one.
3. Restore the heap property by the recursively comparing the new root with its children and swapping it
4. with the higher priority child in the max-heap or the lower priority child in the min heap.
5. Continues this process down the heap until the correct position is found or the leaf is reached.

3. Peek

This operation can be used to returns the element with the highest priority without the removing it from the priority queue.

Algorithm

1. Return the element at the root of the heap.

4. Increase/Decrease Key

This operation can be used to change the priority of the element in the priority queue.

Algorithm

1. Locate the element whose the priority needs to be updated.
2. Update the priority of the element.
3. If the priority is increased in the max-heap or decreased in the min-heap and it can restore the heap property by the heapifying up from the element.
4. If the priority is decreased in the max-heap or increased in the min-heap and restore the heap property by the heapifying down from element.

C Program to Implement Priority Queue

2 dequeued from queue
Top element is 3

Time and Space Complexity

• Time complexity: O(log n), where n is the number of nodes.
• Space complexity: O(n), where n is the number of elements in the priority queue.

Applications of the Priority Queue in C

• It can applies on the Dijkstra's and prim's algorithms is used for the finding the shortest path and minimum spanning tree in graph theory.
• It can used in CPU Scheduling in the operating systems use the priority queues to the manage process scheduling.
• It can applies on the Bandwidth Management used in network routers to manage the packet transmission priority.
• It can applies on Event Simulation for the manages events in the simulations based on their scheduled time.

Conclusion

Priority queues are the versatile and essential the data structures in the computer science. It can useful for any scenario where the elements must be processed according to their importance rather than just their order of the arrival. Efficient implementation of the priority queues particularly using heaps and allowing for the high performance handling of the dynamic priority based data. Make them the indispensable in the fields ranging from the systems design to algorithm optimization.