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Find Length of a Linked List (Iterative and Recursive)

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  • Difficulty Level : Basic
  • Last Updated : 23 Jun, 2022

Write a function to count the number of nodes in a given singly linked list.
 

linkedlist_find_length

For example, the function should return 5 for linked list 1->3->1->2->1.
 

Iterative Solution 

1) Initialize count as 0 
2) Initialize a node pointer, current = head.
3) Do following while current is not NULL
     a) current = current -> next
     b) count++;
4) Return count 

Following are the Iterative implementations of the above algorithm to find the count of nodes in a given singly linked list.
 

C++




// Iterative C++ program to find length
// or count of nodes in a linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
class Node
{
    public:
    int data;
    Node* next;
};
 
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(Node** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node =new Node();
 
    /* put in the data */
    new_node->data = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
 
/* Counts no. of nodes in linked list */
int getCount(Node* head)
{
    int count = 0; // Initialize count
    Node* current = head; // Initialize current
    while (current != NULL)
    {
        count++;
        current = current->next;
    }
    return count;
}
 
/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
 
    /* Use push() to construct below list
    1->2->1->3->1 */
    push(&head, 1);
    push(&head, 3);
    push(&head, 1);
    push(&head, 2);
    push(&head, 1);
 
    /* Check the count function */
    cout<<"count of nodes is "<< getCount(head);
    return 0;
}
 
// This is code is contributed by rathbhupendra


C




// Iterative C program to find length or count of nodes in a linked list
#include<stdio.h>
#include<stdlib.h>
 
/* Link list node */
struct Node
{
    int data;
    struct Node* next;
};
 
/* Given a reference (pointer to pointer) to the head
  of a list and an int, push a new node on the front
  of the list. */
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node =
            (struct Node*) malloc(sizeof(struct Node));
 
    /* put in the data  */
    new_node->data  = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref)    = new_node;
}
 
/* Counts no. of nodes in linked list */
int getCount(struct Node* head)
{
    int count = 0;  // Initialize count
    struct Node* current = head;  // Initialize current
    while (current != NULL)
    {
        count++;
        current = current->next;
    }
    return count;
}
 
/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
 
    /* Use push() to construct below list
     1->2->1->3->1  */
    push(&head, 1);
    push(&head, 3);
    push(&head, 1);
    push(&head, 2);
    push(&head, 1);
 
    /* Check the count function */
    printf("count of nodes is %d", getCount(head));
    return 0;
}


Java




// Java program to count number of nodes in a linked list
 
/* Linked list Node*/
class Node
{
    int data;
    Node next;
    Node(int d)  { data = d;  next = null; }
}
 
// Linked List class
class LinkedList
{
    Node head;  // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCount()
    {
        Node temp = head;
        int count = 0;
        while (temp != null)
        {
            count++;
            temp = temp.next;
        }
        return count;
    }
 
    /* Driver program to test above functions. Ideally
       this function should be in a separate user class.
       It is kept here to keep code compact */
    public static void main(String[] args)
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        System.out.println("Count of nodes is " +
                           llist.getCount());
    }
}


Python3




# A complete working Python program to find length of a
# Linked List iteratively
 
# Node class
class Node:
    # Function to initialise the node object
    def __init__(self, data):
        self.data = data # Assign data
        self.next = None # Initialize next as null
 
 
# Linked List class contains a Node object
class LinkedList:
 
    # Function to initialize head
    def __init__(self):
        self.head = None
 
 
    # This function is in LinkedList class. It inserts
    # a new node at the beginning of Linked List.
    def push(self, new_data):
 
        # 1 & 2: Allocate the Node &
        #     Put in the data
        new_node = Node(new_data)
 
        # 3. Make next of new Node as head
        new_node.next = self.head
 
        # 4. Move the head to point to new Node
        self.head = new_node
 
 
    # This function counts number of nodes in Linked List
    # iteratively, given 'node' as starting node.
    def getCount(self):
        temp = self.head # Initialise temp
        count = 0 # Initialise count
 
        # Loop while end of linked list is not reached
        while (temp):
            count += 1
            temp = temp.next
        return count
 
 
# Code execution starts here
if __name__=='__main__':
    llist = LinkedList()
    llist.push(1)
    llist.push(3)
    llist.push(1)
    llist.push(2)
    llist.push(1)
    print ("Count of nodes is :",llist.getCount())


C#




// C# program to count number
// of nodes in a linked list
using System;
     
/* Linked list Node*/
public class Node
{
    public int data;
    public Node next;
    public Node(int d)
    {
        data = d; next = null;
    }
}
 
// Linked List class
public class LinkedList
{
    Node head; // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCount()
    {
        Node temp = head;
        int count = 0;
        while (temp != null)
        {
            count++;
            temp = temp.next;
        }
        return count;
    }
 
    /* Driver program to test above functions. Ideally
    this function should be in a separate user class.
    It is kept here to keep code compact */
    public static void Main()
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        Console.WriteLine("Count of nodes is " +
                        llist.getCount());
    }
}
 
/* This code contributed by PrinciRaj1992 */


Javascript




<script>
// javascript program to count number of nodes in a linked list
 
/* Linked list Node*/
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}
 
// Linked List class
var head; // head of list
 
    /* Inserts a new Node at front of the list. */
     function push(new_data) {
        /*
         * 1 & 2: Allocate the Node & Put in the data
         */
        var new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
     function getCount() {
        var temp = head;
        var count = 0;
        while (temp != null) {
            count++;
            temp = temp.next;
        }
        return count;
    }
 
    /*
     * Driver program to test above functions. Ideally this function should be in a
     * separate user class. It is kept here to keep code compact
     */
     
        /* Start with the empty list */
        push(1);
        push(3);
        push(1);
        push(2);
        push(1);
 
        document.write("Count of nodes is " + getCount());
 
// This code contributed by Rajput-Ji
</script>


Output

count of nodes is 5

Time complexity: O(n) 

Where n is the size of the linked list, and we have to traverse the list only once.

Auxiliary Space: O(1)

As constant extra space is used.

Recursive Solution 

int getCount(head)
1) If head is NULL, return 0.
2) Else return 1 + getCount(head->next) 

Following are the Recursive implementations of the above algorithm to find the count of nodes in a given singly linked list. 

C++




// Recursive C++ program to find length
// or count of nodes in a linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
class Node {
public:
    int data;
    Node* next;
};
 
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(Node** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node = new Node();
 
    /* put in the data */
    new_node->data = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
 
/* Recursively count number of nodes in linked list */
int getCount(Node* head)
{
    // Base Case
    if (head == NULL) {
        return 0;
    }
    // Count this node plus the rest of the list
    else {
        return 1 + getCount(head->next);
    }
}
 
/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
 
    /* Use push() to construct below list
    1->2->1->3->1 */
    push(&head, 1);
    push(&head, 3);
    push(&head, 1);
    push(&head, 2);
    push(&head, 1);
 
    /* Check the count function */
    cout << "Count of nodes is " << getCount(head);
    return 0;
}
 
// This is code is contributed by rajsanghavi9


Java




// Recursive Java program to count number of nodes in
// a linked list
 
/* Linked list Node*/
class Node
{
    int data;
    Node next;
    Node(int d)  { data = d;  next = null; }
}
 
// Linked List class
class LinkedList
{
    Node head;  // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCountRec(Node node)
    {
        // Base case
        if (node == null)
            return 0;
 
        // Count is this node plus rest of the list
        return 1 + getCountRec(node.next);
    }
 
    /* Wrapper over getCountRec() */
    public int getCount()
    {
        return getCountRec(head);
    }
 
    /* Driver program to test above functions. Ideally
       this function should be in a separate user class.
       It is kept here to keep code compact */
    public static void main(String[] args)
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        System.out.println("Count of nodes is " +
                           llist.getCount());
    }
}


Python3




# A complete working Python program to find length of a
# Linked List recursively
 
# Node class
class Node:
    # Function to initialise the node object
    def __init__(self, data):
        self.data = data  # Assign data
        self.next = None  # Initialize next as null
 
 
# Linked List class contains a Node object
class LinkedList:
 
    # Function to initialize head
    def __init__(self):
        self.head = None
 
 
    # This function is in LinkedList class. It inserts
    # a new node at the beginning of Linked List.
    def push(self, new_data):
 
        # 1 & 2: Allocate the Node &
        #        Put in the data
        new_node = Node(new_data)
 
        # 3. Make next of new Node as head
        new_node.next = self.head
 
        # 4. Move the head to point to new Node
        self.head = new_node
 
    # This function counts number of nodes in Linked List
    # recursively, given 'node' as starting node.
    def getCountRec(self, node):
        if (not node): # Base case
            return 0
        else:
            return 1 + self.getCountRec(node.next)
 
    # A wrapper over getCountRec()
    def getCount(self):
       return self.getCountRec(self.head)
 
# Code execution starts here
if __name__=='__main__':
    llist = LinkedList()
    llist.push(1)
    llist.push(3)
    llist.push(1)
    llist.push(2)
    llist.push(1)
    print ('Count of nodes is :',llist.getCount())


C#




// Recursive C# program to count number of nodes in
// a linked list
using System;
 
 
/* Linked list Node*/
public class Node
{
    public int data;
    public Node next;
    public Node(int d)
    {
        data = d; next = null;
    }
}
 
// Linked List class
public class LinkedList
{
    Node head; // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCountRec(Node node)
    {
        // Base case
        if (node == null)
            return 0;
 
        // Count is this node plus rest of the list
        return 1 + getCountRec(node.next);
    }
 
    /* Wrapper over getCountRec() */
    public int getCount()
    {
        return getCountRec(head);
    }
 
    /* Driver program to test above functions. Ideally
    this function should be in a separate user class.
    It is kept here to keep code compact */
    public static void Main(String[] args)
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        Console.WriteLine("Count of nodes is " +
                        llist.getCount());
    }
}
 
// This code is contributed 29AjayKumar


Javascript




<script>
// Recursive javascript program to count number of nodes in
// a linked list
 
/* Linked list Node*/
class Node {
    constructor(val) {
            this.data = val;
            this.next = null;
        }
    }
 
    // Linked List class
    var head; // head of list
 
    /* Inserts a new Node at front of the list. */
    function push( new_data) {
        /*
         * 1 & 2: Allocate the Node & Put in the data
         */
        var new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
     function getCountRec(node) {
        // Base case
        if (node == null)
            return 0;
 
        // Count is this node plus rest of the list
        return 1 + getCountRec(node.next);
    }
 
    /* Wrapper over getCountRec() */
     function getCount() {
        return getCountRec(head);
    }
 
    /*
     * Driver program to test above functions. Ideally this function should be in a
     * separate user class. It is kept here to keep code compact
     */
     
        /* Start with the empty list */
     
        push(1);
        push(3);
        push(1);
        push(2);
        push(1);
 
        document.write("Count of nodes is " + getCount());
 
// This code contributed by gauravrajput1
</script>


Output

Count of nodes is 5

Time Complexity: O(n)

As we are traversing the linked list only once.

Auxiliary Space: O(n)

Extra space is used in recursion call stack.

The above recursive approach can be modified to make it a tail recursive function and thus our auxiliary space will become O(1):

Implementation of the above approach is given below:

C++




// Tail Recursive C++ program to find length
// or count of nodes in a linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
class Node {
public:
    int data;
    Node* next;
};
 
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(Node** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node = new Node();
 
    /* put in the data */
    new_node->data = new_data;
 
    /* link the old list off the new node */
    new_node->next = (*head_ref);
 
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
// A tail recursive function to count the nodes of a linked
// list
// default value of the count is used as zero
int getCount(Node* head, int count = 0)
{
    // base case
    if (head == NULL)
        return count;
    // move the pointer to next node and increase the count
    return getCount(head->next, count + 1);
}
 
/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
 
    /* Use push() to construct below list
    1->2->1->3->1 */
    push(&head, 1);
    push(&head, 3);
    push(&head, 1);
    push(&head, 2);
    push(&head, 1);
 
    /* Check the count function */
    cout << "Count of nodes is " << getCount(head);
    return 0;
}
 
// This is code is contributed by Abhijeet Kumar


Java




// Tail Recursive Java program to count number of nodes in
// a linked list
 
/* Linked list Node*/
class Node
{
    int data;
    Node next;
    Node(int d)  { data = d;  next = null; }
}
 
// Linked List class
class LinkedList
{
    Node head;  // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCountRec(Node node,int count)
    {
        // Base case
        if (node == null)
            return count;
 
        // Move to the next node and increase count
        return getCountRec(node.next,1+count);
    }
 
    /* Wrapper over getCountRec() */
    public int getCount()
    {
        return getCountRec(head,0);
    }
 
    /* Driver program to test above functions. Ideally
       this function should be in a separate user class.
       It is kept here to keep code compact */
    public static void main(String[] args)
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        System.out.println("Count of nodes is " +
                           llist.getCount());
    }
}
 
// This code was contributed by Abhijeet Kumar(abhijeet19403)


C#




// Tail Recursive C# program to count number of nodes in
// a linked list
using System;
 
/* Linked list Node*/
public class Node {
    public int data;
    public Node next;
    public Node(int d)
    {
        data = d;
        next = null;
    }
}
 
// Linked List class
public class LinkedList {
    Node head; // head of list
 
    /* Inserts a new Node at front of the list. */
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                Put in the data*/
        Node new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
    public int getCountRec(Node node, int count)
    {
        // Base case
        if (node == null)
            return count;
 
        // Move the pointer to next node and increase the
        // count
        return getCountRec(node.next, 1 + count);
    }
 
    /* Wrapper over getCountRec() */
    public int getCount() { return getCountRec(head, 0); }
 
    /* Driver program to test above functions. Ideally
    this function should be in a separate user class.
    It is kept here to keep code compact */
    public static void Main(String[] args)
    {
        /* Start with the empty list */
        LinkedList llist = new LinkedList();
        llist.push(1);
        llist.push(3);
        llist.push(1);
        llist.push(2);
        llist.push(1);
 
        Console.WriteLine("Count of nodes is "
                          + llist.getCount());
    }
}
 
// This code is contributed Abhijeet Kumar(abhijeet19403)


Javascript




<script>
// Tail Recursive javascript program to count number of nodes in
// a linked list
 
/* Linked list Node*/
class Node {
    constructor(val) {
            this.data = val;
            this.next = null;
        }
    }
 
    // Linked List class
    var head; // head of list
 
    /* Inserts a new Node at front of the list. */
    function push( new_data) {
        /*
         * 1 & 2: Allocate the Node & Put in the data
         */
        var new_node = new Node(new_data);
 
        /* 3. Make next of new Node as head */
        new_node.next = head;
 
        /* 4. Move the head to point to new Node */
        head = new_node;
    }
 
    /* Returns count of nodes in linked list */
     function getCountRec(node,var count) {
        // Base case
        if (node == null)
            return count;
 
        // Move the pointer to next node and increase the count
        return getCountRec(node.next,count+1);
    }
 
    /* Wrapper over getCountRec() */
     function getCount() {
        return getCountRec(head,0);
    }
 
    /*
     * Driver program to test above functions. Ideally this function should be in a
     * separate user class. It is kept here to keep code compact
     */
     
        /* Start with the empty list */
     
        push(1);
        push(3);
        push(1);
        push(2);
        push(1);
 
        document.write("Count of nodes is " + getCount());
 
// This code contributed by Abhijeet Kumar(abhijeet19403)
</script>


Output

Count of nodes is 5

Time Complexity: O(n)

As we are traversing the list only once.

Auxiliary Space: O(1)

As we are using tail recursive function, no extra space is used in function call stack .
 

This article is contributed by Ravi. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
 


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