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.
- Create a new node dynamically and insert value into it.
- Check if front==NULL, if it is true then front = rear = (newly created node)
- 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.
- Check whether queue is empty or not means front == NULL.
- If it is empty then display Queue is empty. If queue is not empty then step 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.
Below is the implementation of the above approach:
C++
// C++ program for insertion and// deletion in Circular Queue#include <bits/stdc++.h>using namespace std;// Structure of a Nodestruct Node { int data; struct Node* link;};struct Queue { struct Node *front, *rear;};// Function to create Circular queuevoid 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 Queueint deQueue(Queue* q){ if (q->front == NULL) { cout << "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 Queuevoid displayQueue(struct Queue* q){ struct Node* temp = q->front; cout << endl << "Elements in Circular Queue are: "; while (temp->link != q->front) { cout << temp->data << " "; temp = temp->link; } cout << 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 cout << endl << "Deleted value = " << deQueue(q); cout << endl << "Deleted value = " << 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 Queueimport java.io.*;import java.util.*;public 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 = Noneclass 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 Codeif __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 Queueusing 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 |
Javascript
// Javascript program for insertion and deletion in Circular Queue // Structure of a Node class Node { constructor() { this.data; this.node; } } class Queue { constructor() { this.front; this.rear; } } // Function to create Circular queue function enQueue(q, value) { 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 function deQueue(q) { if (q.front == null) { console.log("Queue is empty"); return Number.MIN_VALUE; } // If this is the last node to be deleted let value; // Value to be dequeued if (q.front == q.rear) { value = q.front.data; q.front = null; q.rear = null; } // There are more than one nodes else { 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 function displayQueue(q) { temp = q.front; console.log("Elements in Circular Queue are: "); while (temp.link != q.front) { console.log(temp.data); temp = temp.link; } console.log(temp.data); } /* Driver of the program */ // Create a queue and initialize front and rear 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 console.log("Deleted value = " + deQueue(q)); console.log("Deleted value = " + deQueue(q)); // Remaining elements in Circular Queue displayQueue(q); enQueue(q, 9); enQueue(q, 20); displayQueue(q); |
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.
Auxiliary Space: O(n) where n is the maximum number of elements that can be stored in the queue.
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.
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