Deletion from a Circular Linked List

We have already discussed about circular linked list and traversal in a circular linked list in the below articles:
Introduction to circular linked list
Traversal in a circular linked list
In this article we will learn about deleting a node from a cicular linked list. Consider the linked list as shown below:
cll_inserted

We will be given a node and our task is to delete that node from the circular linked list.

Examples:



Input : 2->5->7->8->10->(head node)
        data = 5
Output : 2->7->8->10->(head node)

Input : 2->5->7->8->10->(head node)
         7
Output : 2->5->8->10->2(head node)

Algorithm

Case 1: List is empty.

  • If the list is empty we will simply return.

Case 2:List is not empty

  • If the list is not empty then we define two pointers curr and prev and initialize the pointer curr with the head node.
  • Traverse the list using curr to find the node to be deleted and before moving curr to next node, everytime set prev = curr.
  • If the node is found, check if it is the only node in the list. If yes, set head = NULL and free(curr).
  • If the list has more than one node, check if it is the first node of the list. Condition to check this( curr == head). If yes, then move prev until it reaches the last node. After prev reaches the last node, set head = head -> next and prev -> next = head. Delete curr.
  • If curr is not first node, we check if it is the last node in the list. Condition to check this is (curr -> next == head).
  • If curr is the last node. Set prev -> next = head and delete the node curr by free(curr).
  • If the node to be deleted is neither the first node nor the last node, then set prev -> next = temp -> next and delete curr.

Complete program to demonstrate deletion in Circular Linked List:

C++

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// C++ program to delete a given key from
// linked list.
#include <bits/stdc++.h>
using namespace std;
  
/* structure for a node */
class Node {
public:
    int data;
    Node* next;
};
  
/* Function to insert a node at the beginning of 
a Circular linked list */
void push(Node** head_ref, int data)
{
    // Create a new node and make head as next
    // of it.
    Node* ptr1 = new Node();
    ptr1->data = data;
    ptr1->next = *head_ref;
  
    /* If linked list is not NULL then set the 
    next of last node */
    if (*head_ref != NULL) {
        // Find the node before head and update
        // next of it.
        Node* temp = *head_ref;
        while (temp->next != *head_ref)
            temp = temp->next;
        temp->next = ptr1;
    }
    else
        ptr1->next = ptr1; /*For the first node */
  
    *head_ref = ptr1;
}
  
/* Function to print nodes in a given 
circular linked list */
void printList(Node* head)
{
    Node* temp = head;
    if (head != NULL) {
        do {
            cout << temp->data << " ";
            temp = temp->next;
        } while (temp != head);
    }
  
    cout << endl;
}
  
/* Function to delete a given node from the list */
void deleteNode(Node* head, int key)
{
    if (head == NULL)
        return;
  
    // Find the required node
    Node *curr = head, *prev;
    while (curr->data != key) {
        if (curr->next == head) {
            cout << "\nGiven node is not found"
                    " in the list!!!";
            break;
        }
  
        prev = curr;
        curr = curr->next;
    }
  
    // Check if node is only node
    if (curr->next == head) {
        head = NULL;
        free(curr);
        return;
    }
  
    // If more than one node, check if
    // it is first node
    if (curr == head) {
        prev = head;
        while (prev->next != head)
            prev = prev->next;
        head = curr->next;
        prev->next = head;
        free(curr);
    }
  
    // check if node is last node
    else if (curr->next == head) {
        prev->next = head;
        free(curr);
    }
    else {
        prev->next = curr->next;
        free(curr);
    }
}
  
/* Driver program to test above functions */
int main()
{
    /* Initialize lists as empty */
    Node* head = NULL;
  
    /* Created linked list will be 2->5->7->8->10 */
    push(&head, 2);
    push(&head, 5);
    push(&head, 7);
    push(&head, 8);
    push(&head, 10);
  
    cout << "List Before Deletion: ";
    printList(head);
  
    deleteNode(head, 7);
  
    cout << "List After Deletion: ";
    printList(head);
  
    return 0;
}
  
// This is code is contributed by rathbhupendra

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C

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// C program to delete a given key from
// linked list.
#include <stdio.h>
#include <stdlib.h>
  
/* structure for a node */
struct Node {
    int data;
    struct Node* next;
};
  
/* Function to insert a node at the beginning of
   a Circular linked list */
void push(struct Node** head_ref, int data)
{
    // Create a new node and make head as next
    // of it.
    struct Node* ptr1 = (struct Node*)malloc(sizeof(struct Node));
    ptr1->data = data;
    ptr1->next = *head_ref;
  
    /* If linked list is not NULL then set the
       next of last node */
    if (*head_ref != NULL) {
        // Find the node before head and update
        // next of it.
        struct Node* temp = *head_ref;
        while (temp->next != *head_ref)
            temp = temp->next;
        temp->next = ptr1;
    }
    else
        ptr1->next = ptr1; /*For the first node */
  
    *head_ref = ptr1;
}
  
/* Function to print nodes in a given
  circular linked list */
void printList(struct Node* head)
{
    struct Node* temp = head;
    if (head != NULL) {
        do {
            printf("%d ", temp->data);
            temp = temp->next;
        } while (temp != head);
    }
  
    printf("\n");
}
  
/* Function to delete a given node from the list */
void deleteNode(struct Node* head, int key)
{
    if (head == NULL)
        return;
  
    // Find the required node
    struct Node *curr = head, *prev;
    while (curr->data != key) {
        if (curr->next == head) {
            printf("\nGiven node is not found"
                   " in the list!!!");
            break;
        }
  
        prev = curr;
        curr = curr->next;
    }
  
    // Check if node is only node
    if (curr->next == head) {
        head = NULL;
        free(curr);
        return;
    }
  
    // If more than one node, check if
    // it is first node
    if (curr == head) {
        prev = head;
        while (prev->next != head)
            prev = prev->next;
        head = curr->next;
        prev->next = head;
        free(curr);
    }
  
    // check if node is last node
    else if (curr->next == head) {
        prev->next = head;
        free(curr);
    }
    else {
        prev->next = curr->next;
        free(curr);
    }
}
  
/* Driver program to test above functions */
int main()
{
    /* Initialize lists as empty */
    struct Node* head = NULL;
  
    /* Created linked list will be 2->5->7->8->10 */
    push(&head, 2);
    push(&head, 5);
    push(&head, 7);
    push(&head, 8);
    push(&head, 10);
  
    printf("List Before Deletion: ");
    printList(head);
  
    deleteNode(head, 7);
  
    printf("List After Deletion: ");
    printList(head);
  
    return 0;
}

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Java

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// Java program to delete a given key from
// linked list.
class GFG {
  
    /* ure for a node */
    static class Node {
        int data;
        Node next;
    };
  
    /* Function to insert a node at the beginning of 
a Circular linked list */
    static Node push(Node head_ref, int data)
    {
        // Create a new node and make head as next
        // of it.
        Node ptr1 = new Node();
        ptr1.data = data;
        ptr1.next = head_ref;
  
        /* If linked list is not null then set the 
    next of last node */
        if (head_ref != null) {
            // Find the node before head and update
            // next of it.
            Node temp = head_ref;
            while (temp.next != head_ref)
                temp = temp.next;
            temp.next = ptr1;
        }
        else
            ptr1.next = ptr1; /*For the first node */
  
        head_ref = ptr1;
        return head_ref;
    }
  
    /* Function to print nodes in a given 
circular linked list */
    static void printList(Node head)
    {
        Node temp = head;
        if (head != null) {
            do {
                System.out.printf("%d ", temp.data);
                temp = temp.next;
            } while (temp != head);
        }
  
        System.out.printf("\n");
    }
  
    /* Function to delete a given node from the list */
    static Node deleteNode(Node head, int key)
    {
        if (head == null)
            return null;
  
        // Find the required node
        Node curr = head, prev = new Node();
        while (curr.data != key) {
            if (curr.next == head) {
                System.out.printf("\nGiven node is not found"
                                  + " in the list!!!");
                break;
            }
  
            prev = curr;
            curr = curr.next;
        }
  
        // Check if node is only node
        if (curr.next == head) {
            head = null;
            return head;
        }
  
        // If more than one node, check if
        // it is first node
        if (curr == head) {
            prev = head;
            while (prev.next != head)
                prev = prev.next;
            head = curr.next;
            prev.next = head;
        }
  
        // check if node is last node
        else if (curr.next == head) {
            prev.next = head;
        }
        else {
            prev.next = curr.next;
        }
        return head;
    }
  
    /* Driver program to test above functions */
    public static void main(String args[])
    {
        /* Initialize lists as empty */
        Node head = null;
  
        /* Created linked list will be 2.5.7.8.10 */
        head = push(head, 2);
        head = push(head, 5);
        head = push(head, 7);
        head = push(head, 8);
        head = push(head, 10);
  
        System.out.printf("List Before Deletion: ");
        printList(head);
  
        head = deleteNode(head, 7);
  
        System.out.printf("List After Deletion: ");
        printList(head);
    }
}
  
// This code is contributed by Arnab Kundu

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C#

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// C# program to delete a given key from
// linked list.
using System;
  
class GFG {
  
    /* structure for a node */
    public class Node {
        public int data;
        public Node next;
    };
  
    /* Function to insert a node at the beginning of 
a Circular linked list */
    static Node push(Node head_ref, int data)
    {
        // Create a new node and make head as next
        // of it.
        Node ptr1 = new Node();
        ptr1.data = data;
        ptr1.next = head_ref;
  
        /* If linked list is not null then set the 
    next of last node */
        if (head_ref != null) {
            // Find the node before head and update
            // next of it.
            Node temp = head_ref;
            while (temp.next != head_ref)
                temp = temp.next;
            temp.next = ptr1;
        }
        else
            ptr1.next = ptr1; /*For the first node */
  
        head_ref = ptr1;
        return head_ref;
    }
  
    /* Function to print nodes in a given 
circular linked list */
    static void printList(Node head)
    {
        Node temp = head;
        if (head != null) {
            do {
                Console.Write("{0} ", temp.data);
                temp = temp.next;
            } while (temp != head);
        }
  
        Console.Write("\n");
    }
  
    /* Function to delete a given node from the list */
    static Node deleteNode(Node head, int key)
    {
        if (head == null)
            return null;
  
        // Find the required node
        Node curr = head, prev = new Node();
        while (curr.data != key) {
            if (curr.next == head) {
                Console.Write("\nGiven node is not found"
                              + " in the list!!!");
                break;
            }
  
            prev = curr;
            curr = curr.next;
        }
  
        // Check if node is only node
        if (curr.next == head) {
            head = null;
            return head;
        }
  
        // If more than one node, check if
        // it is first node
        if (curr == head) {
            prev = head;
            while (prev.next != head)
                prev = prev.next;
            head = curr.next;
            prev.next = head;
        }
  
        // check if node is last node
        else if (curr.next == head) {
            prev.next = head;
        }
        else {
            prev.next = curr.next;
        }
        return head;
    }
  
    /* Driver code */
    public static void Main(String[] args)
    {
        /* Initialize lists as empty */
        Node head = null;
  
        /* Created linked list will be 2.5.7.8.10 */
        head = push(head, 2);
        head = push(head, 5);
        head = push(head, 7);
        head = push(head, 8);
        head = push(head, 10);
  
        Console.Write("List Before Deletion: ");
        printList(head);
  
        head = deleteNode(head, 7);
  
        Console.Write("List After Deletion: ");
        printList(head);
    }
}
  
// This code has been contributed by 29AjayKumar

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Output:

List Before Deletion: 10 8 7 5 2
List After Deletion: 10 8 5 2

This article is contributed by Harsh Agarwal. 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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