# Delete all the even nodes of a Circular Linked List

• Difficulty Level : Medium
• Last Updated : 10 Jun, 2022

Given a circular singly linked list containing N nodes, the task is to delete all the even nodes from the list. Examples:

```Input : 57->11->2->56->12->61
Output : List after deletion : 57 -> 11 -> 61

Input : 9->11->32->6->13->20
Output : List after deletion : 9 -> 11 -> 13 ```

The idea is to traverse the nodes of the circular singly linked list one by one and get the pointer of the nodes having even data. Delete those nodes by following the approach used in this post.
Below is the implementation of the above idea:

## C++

 `// CPP program to delete all even` `// node from a Circular singly linked list`   `#include ` `using` `namespace` `std;`   `// 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)` `{` `    ``struct` `Node* ptr1 = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));` `    ``struct` `Node* temp = *head_ref;` `    ``ptr1->data = data;` `    ``ptr1->next = *head_ref;`   `    ``// If linked list is not NULL then` `    ``// set the next of last node` `    ``if` `(*head_ref != NULL) {` `        ``while` `(temp->next != *head_ref)` `            ``temp = temp->next;` `        ``temp->next = ptr1;` `    ``}` `    ``else` `        ``ptr1->next = ptr1; ``// For the first node`   `    ``*head_ref = ptr1;` `}`   `// Delete the node if it is even` `void` `deleteNode(Node* head_ref, Node* del)` `{` `    ``struct` `Node* temp = head_ref;` `    ``// If node to be deleted is head node`   `    ``if` `(head_ref == del)` `        ``head_ref = del->next;`   `    ``// traverse list till not found` `    ``// delete node` `    ``while` `(temp->next != del) {` `        ``temp = temp->next;` `    ``}`   `    ``// copy address of node` `    ``temp->next = del->next;`   `    ``// Finally, free the memory occupied by del` `    ``free``(del);` `    ``return``;` `}`   `// Function to delete all even nodes` `// from the singly circular  linked list` `void` `deleteEvenNodes(Node* head)` `{` `    ``struct` `Node* ptr = head;`   `    ``struct` `Node* next;`   `    ``// traverse list till the end` `    ``// if the node is even then delete it` `    ``do` `{` `          ``// point to next node` `        ``next = ptr->next;` `        ``// if node is even` `        ``if` `(ptr->data % 2 == 0)` `            ``deleteNode(head, ptr);` `        ``// get the next node to process` `        ``ptr = next;` `    ``} ``while` `(ptr != head);` `}`   `// Function to print nodes` `void` `printList(``struct` `Node* head)` `{` `    ``struct` `Node* temp = head;` `    ``if` `(head != NULL) {` `        ``do` `{` `            ``printf``(``"%d "``, temp->data);` `            ``temp = temp->next;` `        ``} ``while` `(temp != head);` `    ``}` `}`   `// Driver code` `int` `main()` `{` `    ``// Initialize lists as empty` `    ``struct` `Node* head = NULL;`   `    ``// Created linked list will be 57->11->2->56->12->61` `    ``push(&head, 61);` `    ``push(&head, 12);` `    ``push(&head, 56);` `    ``push(&head, 2);` `    ``push(&head, 11);` `    ``push(&head, 57);`   `    ``cout << ``"\nList after deletion : "``;` `    ``deleteEvenNodes(head);` `    ``printList(head);`   `    ``return` `0;` `}`

## Java

 `// Java program to delete all prime ` `// node from a Circular singly linked list ` `class` `GFG` `{`   `// Structure 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) ` `{ ` `    ``Node ptr1 = ``new` `Node(); ` `    ``Node temp = head_ref; ` `    ``ptr1.data = data; ` `    ``ptr1.next = head_ref; `   `    ``// If linked list is not null then ` `    ``// set the next of last node ` `    ``if` `(head_ref != ``null``) ` `    ``{ ` `        ``while` `(temp.next != head_ref) ` `            ``temp = temp.next; ` `        ``temp.next = ptr1; ` `        ``return` `head_ref;` `    ``} ` `    ``else` `        ``ptr1.next = ptr1; ``// For the first node `   `    ``head_ref = ptr1; ` `return` `head_ref;` `} `   `// Delete the node if it is even ` `static` `Node deleteNode(Node head_ref, Node del) ` `{ ` `    ``Node temp = head_ref; ` `    ``// If node to be deleted is head node `   `    ``if` `(head_ref == del) ` `        ``head_ref = del.next; `   `    ``// traverse list till not found ` `    ``// delete node ` `    ``while` `(temp.next != del)` `    ``{ ` `        ``temp = temp.next; ` `    ``} `   `    ``// copy address of node ` `    ``temp.next = del.next; `   `    ``return` `head_ref; ` `} `   `// Function to delete all even nodes ` `// from the singly circular linked list ` `static` `Node deleteEvenNodes(Node head) ` `{ ` `    ``Node ptr = head; `   `    ``Node next; `   `    ``// traverse list till the end ` `    ``// if the node is even then delete it ` `    ``do` `    ``{ ` `        ``// if node is even ` `        ``if` `(ptr.data % ``2` `== ``0``) ` `            ``deleteNode(head, ptr); `   `        ``// point to next node ` `        ``next = ptr.next; ` `        ``ptr = next; ` `    ``} ` `    ``while` `(ptr != head); ` `    ``return` `head;` `} `   `// Function to print nodes ` `static` `void` `printList(Node head) ` `{ ` `    ``Node temp = head; ` `    ``if` `(head != ``null``)` `    ``{ ` `        ``do` `        ``{ ` `            ``System.out.printf(``"%d "``, temp.data); ` `            ``temp = temp.next; ` `        ``} ` `        ``while` `(temp != head); ` `    ``} ` `} `   `// Driver code ` `public` `static` `void` `main(String args[])` `{ ` `    ``// Initialize lists as empty ` `    ``Node head = ``null``; `   `    ``// Created linked list will be 57.11.2.56.12.61 ` `    ``head=push(head, ``61``); ` `    ``head=push(head, ``12``); ` `    ``head=push(head, ``56``); ` `    ``head=push(head, ``2``); ` `    ``head=push(head, ``11``); ` `    ``head=push(head, ``57``); `   `    ``System.out.println( ``"\nList after deletion : "``); ` `    ``head=deleteEvenNodes(head); ` `    ``printList(head); ` `} ` `}`   `// This code is contributed by Arnab Kundu`

## Python3

 `# Python3 program to delete all even` `# node from a Circular singly linked list` `import` `math`   `# Structure for a node` `class` `Node: ` `    ``def` `__init__(``self``, data): ` `        ``self``.data ``=` `data ` `        ``self``.``next` `=` `None`   `# Function to insert a node at the beginning` `# of a Circular linked list` `def` `push(head_ref, data):` `    ``ptr1 ``=` `Node(data)` `    ``temp ``=` `head_ref` `    ``ptr1.data ``=` `data` `    ``ptr1.``next` `=` `head_ref`   `    ``# If linked list is not None then` `    ``# set the next of last node` `    ``if` `(head_ref !``=` `None``):` `        ``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`   `# Delete the node if it is even` `def` `deleteNode(head_ref, delete):` `    ``temp ``=` `head_ref` `    `  `    ``# If node to be deleted is head node` `    ``if` `(head_ref ``=``=` `delete):` `        ``head_ref ``=` `delete.``next`   `    ``# traverse list till not found` `    ``# delete node` `    ``while` `(temp.``next` `!``=` `delete):` `        ``temp ``=` `temp.``next` `    `  `    ``# copy address of node` `    ``temp.``next` `=` `delete.``next` `    `  `    ``# Finally, free the memory occupied by delete`   `# Function to delete all even nodes` `# from the singly circular linked list` `def` `deleteEvenNodes(head):` `    ``ptr ``=` `head` `    ``next` `=` `None`   `    ``# traverse list till the end` `    ``# if the node is even then delete it` `    ``# if node is even` `    ``next` `=` `ptr.``next` `    ``ptr ``=` `next` `    ``while` `(ptr !``=` `head):` `        ``if` `(ptr.data ``%` `2` `=``=` `0``):` `            ``deleteNode(head, ptr)`   `        ``# point to next node` `        ``next` `=` `ptr.``next` `        ``ptr ``=` `next` `    ``return` `head`   `# Function to print nodes` `def` `printList(head):` `    ``temp ``=` `head` `    ``if` `(head !``=` `None``):` `        ``print``(temp.data, end ``=` `" "``)` `        ``temp ``=` `temp.``next` `        ``while` `(temp !``=` `head):` `            ``print``(temp.data, end ``=` `" "``)` `            ``temp ``=` `temp.``next` `        `  `# Driver code` `if` `__name__``=``=``'__main__'``: ` `    `  `    ``# Initialize lists as empty` `    ``head ``=` `None`   `    ``# Created linked list will be 57.11.2.56.12.61` `    ``head ``=` `push(head, ``61``) ` `    ``head ``=` `push(head, ``12``)` `    ``head ``=` `push(head, ``56``) ` `    ``head ``=` `push(head, ``2``) ` `    ``head ``=` `push(head, ``11``) ` `    ``head ``=` `push(head, ``57``)`   `    ``print``(``"List after deletion : "``, end ``=` `"")` `    ``head ``=` `deleteEvenNodes(head)` `    ``printList(head)` `    `  `# This code is contributed by Srathore`

## C#

 `// C# program to delete all prime ` `// node from a Circular singly 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) ` `{ ` `    ``Node ptr1 = ``new` `Node(); ` `    ``Node temp = head_ref; ` `    ``ptr1.data = data; ` `    ``ptr1.next = head_ref; `   `    ``// If linked list is not null then ` `    ``// set the next of last node ` `    ``if` `(head_ref != ``null``) ` `    ``{ ` `        ``while` `(temp.next != head_ref) ` `            ``temp = temp.next; ` `        ``temp.next = ptr1; ` `        ``return` `head_ref; ` `    ``} ` `    ``else` `        ``ptr1.next = ptr1; ``// For the first node `   `    ``head_ref = ptr1; ` `return` `head_ref; ` `} `   `// Delete the node if it is even ` `static` `Node deleteNode(Node head_ref, Node del) ` `{ ` `    ``Node temp = head_ref; ` `    `  `    ``// If node to be deleted is head node ` `    ``if` `(head_ref == del) ` `        ``head_ref = del.next; `   `    ``// traverse list till not found ` `    ``// delete node ` `    ``while` `(temp.next != del) ` `    ``{ ` `        ``temp = temp.next; ` `    ``} `   `    ``// copy address of node ` `    ``temp.next = del.next; `   `    ``return` `head_ref; ` `} `   `// Function to delete all even nodes ` `// from the singly circular linked list ` `static` `Node deleteEvenNodes(Node head) ` `{ ` `    ``Node ptr = head; `   `    ``Node next; `   `    ``// traverse list till the end ` `    ``// if the node is even then delete it ` `    ``do` `    ``{ ` `        ``// if node is even ` `        ``if` `(ptr.data % 2 == 0) ` `            ``deleteNode(head, ptr); `   `        ``// point to next node ` `        ``next = ptr.next; ` `        ``ptr = next; ` `    ``} ` `    ``while` `(ptr != head); ` `    ``return` `head; ` `} `   `// Function to print nodes ` `static` `void` `printList(Node head) ` `{ ` `    ``Node temp = head; ` `    ``if` `(head != ``null``) ` `    ``{ ` `        ``do` `        ``{ ` `            ``Console.Write(``"{0} "``, temp.data); ` `            ``temp = temp.next; ` `        ``} ` `        ``while` `(temp != head); ` `    ``} ` `} `   `// Driver code ` `public` `static` `void` `Main(String []args) ` `{ ` `    ``// Initialize lists as empty ` `    ``Node head = ``null``; `   `    ``// Created linked list will be 57.11.2.56.12.61 ` `    ``head=push(head, 61); ` `    ``head=push(head, 12); ` `    ``head=push(head, 56); ` `    ``head=push(head, 2); ` `    ``head=push(head, 11); ` `    ``head=push(head, 57); `   `    ``Console.WriteLine( ``"\nList after deletion : "``); ` `    ``head=deleteEvenNodes(head); ` `    ``printList(head); ` `} ` `} `   `// This code has been contributed by 29AjayKumar`

## Javascript

 ``

Output:

`List after deletion : 57 11 61`

Time Complexity: O(N^2)

As to delete each node we need O(N) time and we have to process every node.

Auxiliary Space: O(1)

As constant extra space is used

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