Circular Queue | Set 2 (Circular Linked List Implementation)

Prerequisite – Circular Singly Linked List

We have discussed basics and how to implement circular queue using array in set 1.
Circular Queue | Set 1 (Introduction and Array Implementation)

In this post another method of circular queue implementation is discussed, using Circular Singly Linked List.

Operations on Circular Queue:

Front:Get the front item from queue.
Rear: Get the last item from queue.
enQueue(value) This function is used to insert an element into the circular queue. In a circular queue, the new element is always inserted at Rear position.
1. Create a new node dynamically and insert value into it.
2. Check if front==NULL, if it is true then front = rear = (newly created node)
3. If it is false then rear=(newly created node) and rear node always contains the address of the front node.
deQueue() This function is used to delete an element from the circular queue. In a queue, the element is always deleted from front position.
1. Check whether queue is empty or not means front == NULL.
2. If it is empty then display Queue is empty. If queue is not empty then step 3
3. Check if (front==rear) if it is true then set front = rear = NULL else move the front forward in queue, update address of front in rear node and return the element.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Below is the implementation of above approach:

C++

// C++ program for insertion and 
// deletion in Circular Queue 
#include <bits/stdc++.h> 
using namespace std; 
  
// Structure of a Node 
struct Node { 
    int data; 
    struct Node* link; 
}; 
  
struct Queue { 
    struct Node *front, *rear; 
}; 
  
// Function to create Circular queue 
void enQueue(Queue* q, int value) 
{ 
    struct Node* temp = new Node; 
    temp->data = value; 
    if (q->front == NULL) 
        q->front = temp; 
    else
        q->rear->link = temp; 
  
    q->rear = temp; 
    q->rear->link = q->front; 
} 
  
// Function to delete element from Circular Queue 
int deQueue(Queue* q) 
{ 
    if (q->front == NULL) { 
        printf("Queue is empty"); 
        return INT_MIN; 
    } 
  
    // If this is the last node to be deleted 
    int value; // Value to be dequeued 
    if (q->front == q->rear) { 
        value = q->front->data; 
        free(q->front); 
        q->front = NULL; 
        q->rear = NULL; 
    } 
    else // There are more than one nodes 
    { 
        struct Node* temp = q->front; 
        value = temp->data; 
        q->front = q->front->link; 
        q->rear->link = q->front; 
        free(temp); 
    } 
  
    return value; 
} 
  
// Function displaying the elements of Circular Queue 
void displayQueue(struct Queue* q) 
{ 
    struct Node* temp = q->front; 
    printf("\nElements in Circular Queue are: "); 
    while (temp->link != q->front) { 
        printf("%d ", temp->data); 
        temp = temp->link; 
    } 
    printf("%d", temp->data); 
} 
  
/* Driver of the program */
int main() 
{ 
    // Create a queue and initialize front and rear 
    Queue* q = new Queue; 
    q->front = q->rear = NULL; 
  
    // Inserting elements in Circular Queue 
    enQueue(q, 14); 
    enQueue(q, 22); 
    enQueue(q, 6); 
  
    // Display elements present in Circular Queue 
    displayQueue(q); 
  
    // Deleting elements from Circular Queue 
    printf("\nDeleted value = %d", deQueue(q)); 
    printf("\nDeleted value = %d", deQueue(q)); 
  
    // Remaining elements in Circular Queue 
    displayQueue(q); 
  
    enQueue(q, 9); 
    enQueue(q, 20); 
    displayQueue(q); 
  
    return 0; 
} 

Java

// Java program for insertion and 
// deletion in Circular Queue 
import java.util.*; 
  
class Solution { 
  
    // Structure of a Node 
    static class Node { 
        int data; 
        Node link; 
    } 
  
    static class Queue { 
        Node front, rear; 
    } 
  
    // Function to create Circular queue 
    static void enQueue(Queue q, int value) 
    { 
        Node temp = new Node(); 
        temp.data = value; 
        if (q.front == null) 
            q.front = temp; 
        else
            q.rear.link = temp; 
  
        q.rear = temp; 
        q.rear.link = q.front; 
    } 
  
    // Function to delete element from Circular Queue 
    static int deQueue(Queue q) 
    { 
        if (q.front == null) { 
            System.out.printf("Queue is empty"); 
            return Integer.MIN_VALUE; 
        } 
  
        // If this is the last node to be deleted 
        int value; // Value to be dequeued 
        if (q.front == q.rear) { 
            value = q.front.data; 
            q.front = null; 
            q.rear = null; 
        } 
        else // There are more than one nodes 
        { 
            Node temp = q.front; 
            value = temp.data; 
            q.front = q.front.link; 
            q.rear.link = q.front; 
        } 
  
        return value; 
    } 
  
    // Function displaying the elements of Circular Queue 
    static void displayQueue(Queue q) 
    { 
        Node temp = q.front; 
        System.out.printf("\nElements in Circular Queue are: "); 
        while (temp.link != q.front) { 
            System.out.printf("%d ", temp.data); 
            temp = temp.link; 
        } 
        System.out.printf("%d", temp.data); 
    } 
  
    /* Driver of the program */
    public static void main(String args[]) 
    { 
        // Create a queue and initialize front and rear 
        Queue q = new Queue(); 
        q.front = q.rear = null; 
  
        // Inserting elements in Circular Queue 
        enQueue(q, 14); 
        enQueue(q, 22); 
        enQueue(q, 6); 
  
        // Display elements present in Circular Queue 
        displayQueue(q); 
  
        // Deleting elements from Circular Queue 
        System.out.printf("\nDeleted value = %d", deQueue(q)); 
        System.out.printf("\nDeleted value = %d", deQueue(q)); 
  
        // Remaining elements in Circular Queue 
        displayQueue(q); 
  
        enQueue(q, 9); 
        enQueue(q, 20); 
        displayQueue(q); 
    } 
} 
  
// This code is contributed 
// by Arnab Kundu 

Python3

# Python3 program for insertion and  
# deletion in Circular Queue  
  
# Structure of a Node  
class Node: 
    def __init__(self): 
        self.data = None
        self.link = None
  
class Queue: 
    def __init__(self): 
        front = None
        rear = None
  
# Function to create Circular queue  
def enQueue(q, value): 
    temp = Node()  
    temp.data = value  
    if (q.front == None):  
        q.front = temp  
    else: 
        q.rear.link = temp  
  
    q.rear = temp  
    q.rear.link = q.front 
  
# Function to delete element from  
# Circular Queue  
def deQueue(q): 
    if (q.front == None): 
        print("Queue is empty")  
        return -999999999999
  
    # If this is the last node to be deleted  
    value = None # Value to be dequeued  
    if (q.front == q.rear): 
        value = q.front.data 
        q.front = None
        q.rear = None
    else: # There are more than one nodes  
        temp = q.front  
        value = temp.data  
        q.front = q.front.link  
        q.rear.link = q.front 
  
    return value  
  
# Function displaying the elements  
# of Circular Queue  
def displayQueue(q): 
    temp = q.front  
    print("Elements in Circular Queue are: ",  
                                   end = " ")  
    while (temp.link != q.front): 
        print(temp.data, end = " ")  
        temp = temp.link 
    print(temp.data) 
  
# Driver Code 
if __name__ == '__main__': 
  
    # Create a queue and initialize 
    # front and rear  
    q = Queue()  
    q.front = q.rear = None
  
    # Inserting elements in Circular Queue  
    enQueue(q, 14)  
    enQueue(q, 22)  
    enQueue(q, 6)  
  
    # Display elements present in  
    # Circular Queue  
    displayQueue(q)  
  
    # Deleting elements from Circular Queue  
    print("Deleted value = ", deQueue(q))  
    print("Deleted value = ", deQueue(q))  
  
    # Remaining elements in Circular Queue  
    displayQueue(q)  
  
    enQueue(q, 9)  
    enQueue(q, 20)  
    displayQueue(q) 
  
# This code is contributed by PranchalK 

C#

// C# program for insertion and 
// deletion in Circular Queue 
using System; 
using System.Collections.Generic; 
  
public class GFG { 
  
    // Structure of a Node 
    public class Node { 
        public int data; 
        public Node link; 
    } 
  
    public class LinkedList { 
        public Node front, rear; 
    } 
  
    // Function to create Circular queue 
    public static void enQueue(LinkedList q, 
                               int value) 
    { 
        Node temp = new Node(); 
        temp.data = value; 
        if (q.front == null) { 
            q.front = temp; 
        } 
        else { 
            q.rear.link = temp; 
        } 
  
        q.rear = temp; 
        q.rear.link = q.front; 
    } 
  
    // Function to delete element from 
    // Circular Queue 
    public static int deQueue(LinkedList q) 
    { 
        if (q.front == null) { 
            Console.Write("Queue is empty"); 
            return int.MinValue; 
        } 
  
        // If this is the last node to be deleted 
        int value; // Value to be dequeued 
        if (q.front == q.rear) { 
            value = q.front.data; 
            q.front = null; 
            q.rear = null; 
        } 
        else // There are more than one nodes 
        { 
            Node temp = q.front; 
            value = temp.data; 
            q.front = q.front.link; 
            q.rear.link = q.front; 
        } 
  
        return value; 
    } 
  
    // Function displaying the elements 
    // of Circular Queue 
    public static void displayQueue(LinkedList q) 
    { 
        Node temp = q.front; 
        Console.Write("\nElements in Circular Queue are: "); 
        while (temp.link != q.front) { 
            Console.Write("{0:D} ", temp.data); 
            temp = temp.link; 
        } 
        Console.Write("{0:D}", temp.data); 
    } 
  
    // Driver Code 
    public static void Main(string[] args) 
    { 
        // Create a queue and initialize 
        // front and rear 
        LinkedList q = new LinkedList(); 
        q.front = q.rear = null; 
  
        // Inserting elements in Circular Queue 
        enQueue(q, 14); 
        enQueue(q, 22); 
        enQueue(q, 6); 
  
        // Display elements present in 
        // Circular Queue 
        displayQueue(q); 
  
        // Deleting elements from Circular Queue 
        Console.Write("\nDeleted value = {0:D}", 
                      deQueue(q)); 
        Console.Write("\nDeleted value = {0:D}", 
                      deQueue(q)); 
  
        // Remaining elements in Circular Queue 
        displayQueue(q); 
  
        enQueue(q, 9); 
        enQueue(q, 20); 
        displayQueue(q); 
    } 
} 
  
// This code is contributed by Shrikant13 

Output:

Elements in Circular Queue are: 14 22 6
Deleted value = 14
Deleted value = 22
Elements in Circular Queue are: 6
Elements in Circular Queue are: 6 9 20

Time Complexity: Time complexity of enQueue(), deQueue() operation is O(1) as there is no loop in any of the operation.

Note: In case of linked list implementation, a queue can be easily implemented without being circular. However, in the case of array implementation, we need a circular queue to save space.

This article is contributed by Akash Gupta. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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