C program to Implement a Queue using Linked List
/* * C Program to Implement Queue Data Structure using Linked List */ #include #include struct node { int data; struct node *next; } *front, *back; /* Create an empty queue */ void initialize[] { front = back = NULL; } /* Returns queue size */ int getQueueSize[] { struct node *temp = front; int count = 0; if[front == NULL && back == NULL] return 0; while[temp != back]{ count++; temp = temp->next; } if[temp == back] count++; return count; } /* Returns Frnt Element of the Queue */ int getFrontElement[] { return front->data; } /* Returns the Rear Element of the Queue */ int getBackElement[] { return back->data; } /* Check's if Queue is empty or not */ void isEmpty[] { if [front == NULL && back == NULL] printf["Empty Queue\n"]; else printf["Queue is not Empty\n"]; } /* Adding elements in Queue */ void enqueue[int num] { struct node *temp; temp = [struct node *]malloc[sizeof[struct node]]; temp->data = num; temp->next = NULL; if [back == NULL] { front = back = temp; } else { back->next = temp; back = temp; } } /* Removes an element from front of the queue */ void dequeue[] { struct node *temp; if [front == NULL] { printf["\nQueue is Empty \n"]; return; } else { temp = front; front = front->next; if[front == NULL]{ back = NULL; } printf["Removed Element : %d\n", temp->data]; free[temp]; } } /* Print's Queue */ void printQueue[] { struct node *temp = front; if [[front == NULL] && [back == NULL]] { printf["Queue is Empty\n"]; return; } while [temp != NULL] { printf["%d", temp->data]; temp = temp->next; if[temp != NULL] printf["-->"]; } } int main[] { /* Initializing Queue */ initialize[]; /* Adding elements in Queue */ enqueue[1]; enqueue[3]; enqueue[7]; enqueue[5]; enqueue[10]; /* Printing Queue */ printQueue[]; /* Printing size of Queue */ printf["\nSize of Queue : %d\n", getQueueSize[]]; /* Printing front and rear element of Queue */ printf["Front Element : %d\n", getFrontElement[]]; printf["Rear Element : %d\n", getBackElement[]]; /* Removing Elementd from Queue */ dequeue[]; dequeue[]; dequeue[]; dequeue[]; dequeue[]; dequeue[]; return 0; } Output1-->3-->7-->5-->10 Size of Queue : 5 Front Element : 1 Rear Element : 10 Removed Element : 1 Removed Element : 3 Removed Element : 7 Removed Element : 5 Removed Element : 10 Queue is Empty
Queue using linked list
Queue using an array - drawback
If we implement the queue using an array, we need to specify the array size at the beginning[at compile time].
We can't change the size of an array at runtime. So, the queue will only work for a fixed number of elements.
Solution
We can implement the queue data structure using the linked list.
In the linked list, we can change its size at runtime.
Queue – Linked List Implementation
In the previous post, we introduced Queue and discussed array implementation. In this post, linked list implementation is discussed. The following two main operations must be implemented efficiently.
In a Queue data structure, we maintain two pointers, front and rear. The front points the first item of queue and rear points to last item.
enQueue[] This operation adds a new node after rear and moves rear to the next node.
deQueue[] This operation removes the front node and moves front to the next node.
Linked List implementation of Queue
Due to the drawbacks discussed in the previous section of this tutorial, the array implementation can not be used for the large scale applications where the queues are implemented. One of the alternative of array implementation is linked list implementation of queue.
The storage requirement of linked representation of a queue with n elements is o[n] while the time requirement for operations is o[1].
In a linked queue, each node of the queue consists of two parts i.e. data part and the link part. Each element of the queue points to its immediate next element in the memory.
In the linked queue, there are two pointers maintained in the memory i.e. front pointer and rear pointer. The front pointer contains the address of the starting element of the queue while the rear pointer contains the address of the last element of the queue.
Insertion and deletions are performed at rear and front end respectively. If front and rear both are NULL, it indicates that the queue is empty.
The linked representation of queue is shown in the following figure.
Implementation of Queues using Linked List in C
July 27, 2020
Implement queue operations using linked list
Write a C program to implement queue operations using linked list. Here’s simpleprogram to implement queue operations using linked list in C Programming Language.