# Delete all Non-Prime Nodes from a Singly Linked List

Given a singly linked list containing N nodes, the task is to delete all nodes from the list which are not prime.

Examples:

Input : List = 15 -> 16 -> 6 -> 7 -> 17
Output : Final List = 7 -> 17

Input : List = 15 -> 3 -> 4 -> 2 -> 9
Output : Final List = 3 ->2

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

Approach: The idea is to traverse the nodes of the singly linked list one by one and get the pointer of the nodes which are not prime. Delete those nodes by following the approach used in the post: Delete a node from Linked List.

Below is the implementation of above idea:

## C++

 `// C++ implementation to delete all ` `// non-prime nodes from the singly ` `// linked list ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// Node of the singly linked list ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// function to insert a node at the beginning ` `// of the singly Linked List ` `void` `push(Node** head_ref, ``int` `new_data) ` `{ ` `    ``Node* new_node = ``new` `Node; ` `    ``new_node->data = new_data; ` `    ``new_node->next = (*head_ref); ` `    ``(*head_ref) = new_node; ` `} ` ` `  `// Function to check if a number is prime ` `bool` `isPrime(``int` `n) ` `{ ` `    ``// Corner cases ` `    ``if` `(n <= 1) ` `        ``return` `false``; ` `    ``if` `(n <= 3) ` `        ``return` `true``; ` ` `  `    ``// This is checked so that we can skip ` `    ``// middle five numbers in below loop ` `    ``if` `(n % 2 == 0 || n % 3 == 0) ` `        ``return` `false``; ` ` `  `    ``for` `(``int` `i = 5; i * i <= n; i = i + 6) ` `        ``if` `(n % i == 0 || n % (i + 2) == 0) ` `            ``return` `false``; ` ` `  `    ``return` `true``; ` `} ` ` `  `// function to delete all non-prime nodes ` `// from the singly linked list ` `void` `deleteNonPrimeNodes(Node** head_ref) ` `{ ` `    ``// Remove all composite nodes at the beginning ` `    ``Node* ptr = *head_ref; ` `    ``while` `(ptr != NULL && !isPrime(ptr->data)) ` `    ``{ ` `       ``Node *temp = ptr; ` `       ``ptr = ptr->next; ` `       ``delete``(temp); ` `    ``} ` `    ``*head_ref = ptr; ` `    ``if` `(ptr == NULL) ` `       ``return``; ` ` `  `    ``// Remove remaining nodes ` `    ``Node *curr = ptr->next; ` `    ``while` `(curr != NULL) { ` ` `  `        ``if` `(!isPrime(curr->data)) ` `        ``{ ` `            ``ptr->next = curr->next; ` `            ``delete``(curr); ` `            ``curr = ptr->next; ` `        ``} ` `        ``else` `        ``{ ` `            ``ptr = curr; ` `            ``curr = curr->next; ` `        ``} ` `     ``}     ` `} ` ` `  `// function to print nodes in a ` `// given singly linked list ` `void` `printList(Node* head) ` `{ ` `    ``while` `(head != NULL) { ` `        ``cout << head->data << ``" "``; ` `        ``head = head->next; ` `    ``} ` `} ` ` `  `// Driver program ` `int` `main() ` `{ ` `    ``// start with the empty list ` `    ``Node* head = NULL; ` ` `  `    ``// create the linked list ` `    ``// 15 -> 16 -> 7 -> 6 -> 17 ` `    ``push(&head, 17); ` `    ``push(&head, 7); ` `    ``push(&head, 6); ` `    ``push(&head, 16); ` `    ``push(&head, 15); ` ` `  `    ``cout << ``"Original List: "``; ` `    ``printList(head); ` ` `  `    ``deleteNonPrimeNodes(&head); ` ` `  `    ``cout << ``"\nModified List: "``; ` `    ``printList(head); ` `} `

## Java

 `// Java implementation to delete all  ` `// non-prime nodes from the singly  ` `// linked list ` `class` `GFG ` `{ ` `     `  `// Node of the singly linked list  ` `static` `class` `Node ` `{  ` `    ``int` `data;  ` `    ``Node next;  ` `};  ` ` `  `// function to insert a node at the beginning  ` `// of the singly Linked List  ` `static` `Node push(Node head_ref, ``int` `new_data)  ` `{  ` `    ``Node new_node = ``new` `Node();  ` `    ``new_node.data = new_data;  ` `    ``new_node.next = (head_ref);  ` `    ``(head_ref) = new_node;  ` `    ``return` `head_ref; ` `}  ` ` `  `// Function to check if a number is prime  ` `static` `boolean` `isPrime(``int` `n)  ` `{  ` `    ``// Corner cases  ` `    ``if` `(n <= ``1``)  ` `        ``return` `false``;  ` `    ``if` `(n <= ``3``)  ` `        ``return` `true``;  ` ` `  `    ``// This is checked so that we can skip  ` `    ``// middle five numbers in below loop  ` `    ``if` `(n % ``2` `== ``0` `|| n % ``3` `== ``0``)  ` `        ``return` `false``;  ` ` `  `    ``for` `(``int` `i = ``5``; i * i <= n; i = i + ``6``)  ` `        ``if` `(n % i == ``0` `|| n % (i + ``2``) == ``0``)  ` `            ``return` `false``;  ` ` `  `    ``return` `true``;  ` `}  ` ` `  `// function to delete all non-prime nodes  ` `// from the singly linked list  ` `static` `Node deleteNonPrimeNodes(Node head_ref)  ` `{  ` `    ``// Remove all composite nodes at the beginning  ` `    ``Node ptr = head_ref;  ` `    ``while` `(ptr != ``null` `&& !isPrime(ptr.data))  ` `    ``{  ` `        ``Node temp = ptr;  ` `        ``ptr = ptr.next;  ` `    ``}  ` `    ``head_ref = ptr;  ` `    ``if` `(ptr == ``null``)  ` `        ``return` `null``;  ` ` `  `    ``// Remove remaining nodes  ` `    ``Node curr = ptr.next;  ` `    ``while` `(curr != ``null``)  ` `    ``{  ` ` `  `        ``if` `(!isPrime(curr.data))  ` `        ``{  ` `            ``ptr.next = curr.next;  ` `            ``curr = ptr.next;  ` `        ``}  ` `        ``else` `        ``{  ` `            ``ptr = curr;  ` `            ``curr = curr.next;  ` `        ``}  ` `    ``}  ` `    ``return` `head_ref; ` `}  ` ` `  `// function to print nodes in a  ` `// given singly linked list  ` `static` `void` `printList(Node head)  ` `{  ` `    ``while` `(head != ``null``) ` `    ``{  ` `        ``System.out.print(head.data + ``" "``);  ` `        ``head = head.next;  ` `    ``}  ` `}  ` ` `  `// Driver code  ` `public` `static` `void` `main(String args[])  ` `{  ` `    ``// start with the empty list  ` `    ``Node head = ``null``;  ` ` `  `    ``// create the linked list  ` `    ``// 15 . 16 . 7 . 6 . 17  ` `    ``head = push(head, ``17``);  ` `    ``head = push(head, ``7``);  ` `    ``head = push(head, ``6``);  ` `    ``head = push(head, ``16``);  ` `    ``head = push(head, ``15``);  ` ` `  `    ``System.out.print(``"Original List: "``);  ` `    ``printList(head);  ` ` `  `    ``head = deleteNonPrimeNodes(head);  ` ` `  `    ``System.out.print(``"\nModified List: "``);  ` `    ``printList(head);  ` `}  ` `} ` ` `  `// This code is contributed by Arnab Kundu `

## Python3

 `# Python3 implementation to delete all ` `# non-prime nodes from the singly ` `# linked list ` `import` `math  ` ` `  `# Node of the singly linked list ` `class` `Node:  ` `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data  ` `        ``self``.``next` `=` `None` ` `  `# function to insert a node at the beginning ` `# of the singly Linked List ` `def` `push(head_ref, new_data): ` `    ``new_node ``=` `Node(new_data) ` `    ``new_node.data ``=` `new_data ` `    ``new_node.``next` `=` `head_ref ` `    ``head_ref ``=` `new_node ` `    ``return` `head_ref ` ` `  `# Function to check if a number is prime ` `def` `isPrime(n): ` `     `  `    ``# Corner cases ` `    ``if` `(n <``=` `1``): ` `        ``return` `False` `    ``if` `(n <``=` `3``): ` `        ``return` `True` ` `  `    ``# This is checked so that we can skip ` `    ``# middle five numbers in below loop ` `    ``if` `(n ``%` `2` `=``=` `0` `or` `n ``%` `3` `=``=` `0``): ` `        ``return` `False` `    ``for` `i ``in` `range``(``5``, n ``+` `1``, ``6``): ` `        ``if` `(i ``*` `i < n ``+` `2` `and`  `           ``(n ``%` `i ``=``=` `0` `or` `n ``%` `(i ``+` `2``) ``=``=` `0``)): ` `            ``return` `False` `         `  `    ``return` `True` ` `  `# function to delete all non-prime nodes ` `# from the singly linked list ` `def` `deleteNonPrimeNodes(head_ref): ` `     `  `    ``# Remove all composite nodes at the beginning ` `    ``ptr ``=` `head_ref ` `    ``while` `(ptr !``=` `None` `and`  `           ``isPrime(ptr.data)!``=` `True``): ` `        ``temp ``=` `ptr ` `        ``ptr ``=` `ptr.``next` `        ``# delete(temp) ` `     `  `    ``head_ref ``=` `ptr ` `    ``if` `(ptr ``=``=` `None``): ` `        ``return` `None` ` `  `    ``# Remove remaining nodes ` `    ``curr ``=` `ptr.``next` `    ``while` `(curr !``=` `None``) : ` ` `  `        ``if` `(isPrime(curr.data) !``=` `True``): ` `            ``ptr.``next` `=` `curr.``next` `            ``#delete(curr) ` `            ``curr ``=` `ptr.``next` `         `  `        ``else``: ` `            ``ptr ``=` `curr ` `            ``curr ``=` `curr.``next` `         `  `        ``return` `head_ref      ` ` `  `# function to print nodes in a ` `# given singly linked list ` `def` `printList( head): ` `    ``while` `(head !``=` `None``) : ` `        ``print``(head.data, end ``=` `" "``) ` `        ``head ``=` `head.``next` `     `  `# Driver Code ` `if` `__name__``=``=``'__main__'``:  ` ` `  `    ``# start with the empty list ` `    ``head ``=` `None` ` `  `    ``# create the linked list ` `    ``# 15 -> 16 -> 7 -> 6 -> 17 ` `    ``head ``=` `push(head, ``17``) ` `    ``head ``=` `push(head, ``7``) ` `    ``head ``=` `push(head, ``6``) ` `    ``head ``=` `push(head, ``16``) ` `    ``head ``=` `push(head, ``15``) ` ` `  `    ``print``(``"Original List: "``) ` `    ``printList(head) ` ` `  `    ``head ``=` `deleteNonPrimeNodes(head) ` ` `  `    ``print``(``"\nModified List: "``) ` `    ``printList(head) ` ` `  `# This code is contributed by AbhiThakur `

## C#

 `// C# implementation to delete all  ` `// non-prime nodes from the singly  ` `// linked list  ` `using` `System; ` ` `  `class` `GFG  ` `{ ` ` `  `    ``// Node of the singly linked list  ` `    ``public` `class` `Node  ` `    ``{ ` `        ``public` `int` `data; ` `        ``public` `Node next; ` `    ``}; ` ` `  `    ``// function to insert a node at the beginning  ` `    ``// of the singly Linked List  ` `    ``static` `Node push(Node head_ref, ``int` `new_data)  ` `    ``{ ` `        ``Node new_node = ``new` `Node(); ` `        ``new_node.data = new_data; ` `        ``new_node.next = (head_ref); ` `        ``(head_ref) = new_node; ` `        ``return` `head_ref; ` `    ``} ` ` `  `    ``// Function to check if a number is prime  ` `    ``static` `bool` `isPrime(``int` `n) ` `    ``{ ` `        ``// Corner cases  ` `        ``if` `(n <= 1)  ` `        ``{ ` `            ``return` `false``; ` `        ``} ` `        ``if` `(n <= 3)  ` `        ``{ ` `            ``return` `true``; ` `        ``} ` ` `  `        ``// This is checked so that we can skip  ` `        ``// middle five numbers in below loop  ` `        ``if` `(n % 2 == 0 || n % 3 == 0)  ` `        ``{ ` `            ``return` `false``; ` `        ``} ` ` `  `        ``for` `(``int` `i = 5; i * i <= n; i = i + 6)  ` `        ``{ ` `            ``if` `(n % i == 0 || n % (i + 2) == 0) ` `            ``{ ` `                ``return` `false``; ` `            ``} ` `        ``} ` `        ``return` `true``; ` `    ``} ` ` `  `    ``// function to delete all non-prime nodes  ` `    ``// from the singly linked list  ` `    ``static` `Node deleteNonPrimeNodes(Node head_ref)  ` `    ``{ ` `        ``// Remove all composite nodes ` `        ``// at the beginning  ` `        ``Node ptr = head_ref; ` `        ``while` `(ptr != ``null` `&& !isPrime(ptr.data)) ` `        ``{ ` `            ``Node temp = ptr; ` `            ``ptr = ptr.next; ` `        ``} ` `        ``head_ref = ptr; ` `        ``if` `(ptr == ``null``)  ` `        ``{ ` `            ``return` `null``; ` `        ``} ` ` `  `        ``// Remove remaining nodes  ` `        ``Node curr = ptr.next; ` `        ``while` `(curr != ``null``)  ` `        ``{ ` `            ``if` `(!isPrime(curr.data)) ` `            ``{ ` `                ``ptr.next = curr.next; ` `                ``curr = ptr.next; ` `            ``}  ` `            ``else`  `            ``{ ` `                ``ptr = curr; ` `                ``curr = curr.next; ` `            ``} ` `        ``} ` `        ``return` `head_ref; ` `    ``} ` ` `  `    ``// function to print nodes in a  ` `    ``// given singly linked list  ` `    ``static` `void` `printList(Node head) ` `    ``{ ` `        ``while` `(head != ``null``)  ` `        ``{ ` `            ``Console.Write(head.data + ``" "``); ` `            ``head = head.next; ` `        ``} ` `    ``} ` ` `  `    ``// Driver code  ` `    ``public` `static` `void` `Main(String[] args)  ` `    ``{ ` `        ``// start with the empty list  ` `        ``Node head = ``null``; ` ` `  `        ``// create the linked list  ` `        ``// 15 . 16 . 7 . 6 . 17  ` `        ``head = push(head, 17); ` `        ``head = push(head, 7); ` `        ``head = push(head, 6); ` `        ``head = push(head, 16); ` `        ``head = push(head, 15); ` ` `  `        ``Console.Write(``"Original List: "``); ` `        ``printList(head); ` ` `  `        ``head = deleteNonPrimeNodes(head); ` ` `  `        ``Console.Write(``"\nModified List: "``); ` `        ``printList(head); ` `    ``} ` `}  ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```Original List: 15 16 6 7 17
Modified List: 7 17
```

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