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



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++

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// C++ implementation to delete all
// non-prime nodes from the singly
// linked list
#include <bits/stdc++.h>
  
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);
}

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Java

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// 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

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Output:

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


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