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.
  Steps:
  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.
  Steps:
  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.

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