Count of Prime Nodes of a Singly Linked List

Given a singly linked list containing N nodes, the task is to find the total count of prime numbers.

Examples:

Input: List = 15 -> 5 -> 6 -> 10 -> 17
Output: 2
5 and 17 are the prime nodes

Input: List = 29 -> 3 -> 4 -> 2 -> 9
Output: 3
2, 3 and 29 are the prime nodes

Approach: The idea is to traverse the linked list to the end and check if the current node is prime or not. If YES, increment the count by 1 and keep doing the same until all the nodes get traversed.

Below is the implementation of above approach:

C++



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// C++ implementation to find count of prime numbers
// in 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 find count of prime
// nodes in a linked list
int countPrime(Node** head_ref)
{
    int count = 0;
    Node* ptr = *head_ref;
  
    while (ptr != NULL) {
        // If current node is prime
        if (isPrime(ptr->data)) {
            // Update count
            count++;
        }
        ptr = ptr->next;
    }
  
    return count;
}
  
// Driver program
int main()
{
    // start with the empty list
    Node* head = NULL;
  
    // create the linked list
    // 15 -> 5 -> 6 -> 10 -> 17
    push(&head, 17);
    push(&head, 10);
    push(&head, 6);
    push(&head, 5);
    push(&head, 15);
  
    // Function call to print require answer
    cout << "Count of prime nodes = "
         << countPrime(&head);
  
    return 0;
}

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Java

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// Java implementation to find count of prime numbers 
// in the singly linked list 
class solution
{
  
// 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 find count of prime 
// nodes in a linked list 
static int countPrime(Node   head_ref) 
    int count = 0
    Node  ptr =  head_ref; 
  
    while (ptr != null) { 
        // If current node is prime 
        if (isPrime(ptr.data)) { 
            // Update count 
            count++; 
        
        ptr = ptr.next; 
    
  
    return count; 
  
// Driver program 
public static void main(String args[])
    // start with the empty list 
    Node  head = null
  
    // create the linked list 
    // 15 . 5 . 6 . 10 . 17 
    head=push(head, 17); 
    head=push(head, 10); 
    head=push(head, 6); 
    head=push(head, 5); 
    head=push(head, 15); 
  
    // Function call to print require answer 
    System.out.print( "Count of prime nodes = "+ countPrime(head)); 
  
}
  
// This code is contributed by Arnab Kundu

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Python3

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# Python3 implementation to find count of 
# prime numbers in the singly linked list
  
# 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
      
    i = 5
    while i * i <= n: 
        if n % i == 0 or n % (i + 2) == 0
            return False
        i += 6
  
    return True
  
# Link list node
class Node: 
      
    def __init__(self, data, next):
        self.data = data
        self.next = next
          
class LinkedList:
      
    def __init__(self):
        self.head = None
      
    # Push a new node on the front of the list.     
    def push(self, new_data):
        new_node = Node(new_data, self.head)
        self.head = new_node
  
    # Function to find count of prime 
    # nodes in a linked list 
    def countPrime(self): 
      
        count = 0
        ptr = self.head 
      
        while ptr != None
              
            # If current node is prime 
            if isPrime(ptr.data): 
                  
                # Update count 
                count += 1
              
            ptr = ptr.next
      
        return count 
  
# Driver Code
if __name__ == "__main__":
  
    # Start with the empty list
    linkedlist = LinkedList()
  
    # create the linked list 
    # 15 -> 5 -> 6 -> 10 -> 17 
    linkedlist.push(17
    linkedlist.push(10
    linkedlist.push(6
    linkedlist.push(5
    linkedlist.push(15
  
    # Function call to print require answer 
    print("Count of prime nodes =",
           linkedlist.countPrime()) 
  
# This code is contributed by Rituraj Jain

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C#

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// C# implementation to find count of prime numbers 
// in 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 find count of prime 
// nodes in a linked list 
static int countPrime(Node head_ref) 
    int count = 0; 
    Node ptr = head_ref; 
  
    while (ptr != null
    
        // If current node is prime 
        if (isPrime(ptr.data)) 
        
            // Update count 
            count++; 
        
        ptr = ptr.next; 
    
  
    return count; 
  
// Driver code 
public static void Main(String []args)
    // start with the empty list 
    Node head = null
  
    // create the linked list 
    // 15 . 5 . 6 . 10 . 17 
    head=push(head, 17); 
    head=push(head, 10); 
    head=push(head, 6); 
    head=push(head, 5); 
    head=push(head, 15); 
  
    // Function call to print require answer 
    Console.Write( "Count of prime nodes = "+ countPrime(head)); 
}
  
// This code has been contributed by 29AjayKumar

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Output:

Count of prime nodes = 2

Time Complexity: O(N*sqrt(P)), where N is length of the LinkedList and P is the maximum element in the List

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