Count nodes in Circular linked list

Given a circular linked list, count the number of nodes in it. For example, the output is 5 for the below list. 

Approach: We use the concept used in Circular Linked List | Set 2 (Traversal). While traversing, we keep track of the count of nodes. 

C++

// C++  program to count number of nodes in a circular
// linked list.
#include <bits/stdc++.h>
using namespace std;

/*structure for a node*/

struct Node {
    int data;
    Node* next;
    Node(int x)
    {
        data = x;
        next = NULL;
    }
};
/* Function to insert a node at the beginning
of a Circular linked list */
struct Node* push(struct Node* last, int data)
{
    if (last == NULL) {
        struct Node* temp
            = (struct Node*)malloc(sizeof(struct Node));

        // Assigning the data.
        temp->data = data;
        last = temp;
        // Note : list was empty. We link single node
        // to itself.
        temp->next = last;

        return last;
    }

    // Creating a node dynamically.
    struct Node* temp
        = (struct Node*)malloc(sizeof(struct Node));

    // Assigning the data.
    temp->data = data;

    // Adjusting the links.
    temp->next = last->next;
    last->next = temp;

    return last;
}

/* Function to  count  nodes in a given Circular
linked list */

int countNodes(Node* head)
{
    Node* temp = head;
    int result = 0;
    if (head != NULL) {
        do {
            temp = temp->next;
            result++;
        } while (temp != head);
    }

    return result;
}

/* Driver program to test above functions */
int main()
{
    /* Initialize lists as empty */
    Node* head = NULL;
    head = push(head, 12);
    head = push(head, 56);
    head = push(head, 2);
    head = push(head, 11);
    cout << countNodes(head);
    return 0;
}

// This code is contributed by anushikaseth

C

// C program to count number of nodes in a circular linked
// list.
#include <stdio.h>
#include <stdlib.h>

/*structure for a node*/
typedef struct Node {
    int data;
    struct Node* next;
} Node;

/* Function to insert a node at the beginning of a Circular
   linked list */
void push(Node** head_ref, int data)
{
    Node* ptr1 = (Node*)malloc(sizeof(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;
    }
    else
        ptr1->next = ptr1; /*For the first node */
    *head_ref = ptr1;
}

/* Function to  count  nodes in a given Circular
linked list */

int countNodes(Node* head)
{
    Node* temp = head;
    int result = 0;
    if (head != NULL) {
        do {
            temp = temp->next;
            result++;
        } while (temp != head);
    }

    return result;
}

/* Driver program to test above functions */
int main()
{
    /* Initialize lists as empty */
    Node* head = NULL;
    push(&head, 12);
    push(&head, 56);
    push(&head, 2);
    push(&head, 11);
    printf("%d", countNodes(head));
    return 0;
}

// This code is contributed by Aditya Kumar (adityakumar129)

Java

// Java program to count number of nodes in
// a circular linked list.
import java.util.*;
import java.io.*;

public 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)
{
    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;
    } 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 int countNodes( Node head)
{
    Node temp = head;
    int result = 0;
    if (head != null)
    {
        do
        {
            temp = temp.next;
            result++;
        } while (temp != head);
    }

    return result;
}

/* Driver program to test above functions */
public static void main(String args[])
{
    /* Initialize lists as empty */
    Node head = null;
    head = push(head, 12);
    head = push(head, 56);
    head = push(head, 2);
    head = push(head, 11);

    System.out.printf("%d", countNodes(head));
}
}

// This code is contributed by Arnab Kundu

Python3

# Python3 program to count number of nodes in
# a circular linked list.

# 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(0)
    temp = head_ref
    ptr1.data = data
    ptr1.next = head_ref

    # If the 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

# Function to print nodes
# in a given Circular linked list
def countNodes(head):

    temp = head
    result = 0
    if (head != None) :
        while True :
            temp = temp.next
            result = result + 1
            if (temp == head):
                break

    return result

# Driver Code
if __name__=='__main__':

    # Initialize lists as empty */
    head = None
    head = push(head, 12)
    head = push(head, 56)
    head = push(head, 2)
    head = push(head, 11)

    print( countNodes(head))

# This code is contributed by Arnab Kundu

C#

// C# program to count number of nodes in
// a circular 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;
    } 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 int countNodes( Node head)
{
    Node temp = head;
    int result = 0;
    if (head != null)
    {
        do
        {
            temp = temp.next;
            result++;
        } while (temp != head);
    }

    return result;
}

/* Driver code */
public static void Main(String []args)
{
    /* Initialize lists as empty */
    Node head = null;
    head = push(head, 12);
    head = push(head, 56);
    head = push(head, 2);
    head = push(head, 11);

    Console.Write( countNodes(head));
}
}

// This code is contributed by Arnab Kundu

Javascript

<script>
// javascript program to count number of nodes in
// a circular linked list.     /* ure for a node */
class Node {
    constructor() {
        this.data = 0;
        this.next = null;
    }
}
    /*
     * Function to insert a node at the beginning of a Circular linked list
     */
    function push(head_ref , data) {
    var ptr1 = new Node();
    var 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;
        return head_ref;
    }

    /*
     * Function to print nodes in a given Circular linked list
     */
    function countNodes(head) {
    var temp = head;
        var result = 0;
        if (head != null) {
            do {
                temp = temp.next;
                result++;
            } while (temp != head);
        }

        return result;
    }

    /* Driver program to test above functions */

        /* Initialize lists as empty */
        var head = null;
        head = push(head, 12);
        head = push(head, 56);
        head = push(head, 2);
        head = push(head, 11);

        document.write(countNodes(head));

// This code contributed by umadevi9616
</script>

Output

4

Time Complexity: O(n), As we are visiting every node just once.
Auxiliary Space: O(1), As constant extra space is used

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