Write a function to count the number of nodes in a given singly linked list
Examples:
Input:
Input: 2->4->1->9->5->3->6
Output: 7
An iterative approach for finding the length of the linked list:
Follow the given steps to solve the problem:
- Initialize count as 0
- Initialize a node pointer, current = head.
-
Do following while current is not NULL
- current = current -> next
- Increment count by 1.
- Return count
Below is the implementation of the above approach:
// 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 of 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 code*/ 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);
// Function call
cout << "count of nodes is " << getCount(head);
return 0;
} // This is code is contributed by rathbhupendra |
// 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 of 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 code*/ 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);
// Function call
printf ( "count of nodes is %d" , getCount(head));
return 0;
} |
// 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 code
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 );
// Function call
System.out.println( "Count of nodes is "
+ llist.getCount());
}
} |
# 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
# Driver code if __name__ = = '__main__' :
llist = LinkedList()
llist.push( 1 )
llist.push( 3 )
llist.push( 1 )
llist.push( 2 )
llist.push( 1 )
# Function call
print ( "Count of nodes is :" , llist.getCount())
|
// 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 code
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);
// Function call
Console.WriteLine( "Count of nodes is "
+ llist.getCount());
}
} /* This code contributed by PrinciRaj1992 */ |
<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> |
count of nodes is 5
Time complexity: O(N), Where N is the size of the linked list
Auxiliary Space: O(1), As constant extra space is used.
A recursive approach for finding the length of the linked list:
Follow the given steps to solve the problem:
- If the head is NULL, return 0.
- Otherwise, return 1 + getCount(head->next)
Below is the implementation of the above approach:
// 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 of 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 |
// 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());
}
} |
# 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())
|
// 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 |
<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> |
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 the recursion call stack.
Recursive approach for finding the length of the linked list using constant space:
To solve the problem follow the below idea:
The above recursive approach can be modified to make it a tail recursive function and thus our auxiliary space will become O(1)
Below is the implementation of the above approach:
// 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 of 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 code*/ 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);
// Function call
cout << "Count of nodes is " << getCount(head);
return 0;
} // This is code is contributed by Abhijeet Kumar |
// 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 code
public static void main(String[] args)
{
LinkedList llist = new LinkedList();
llist.push( 1 );
llist.push( 3 );
llist.push( 1 );
llist.push( 2 );
llist.push( 1 );
// Function call
System.out.println( "Count of nodes is "
+ llist.getCount());
}
} // This code was contributed by Abhijeet // Kumar(abhijeet19403) |
# A complete working Python3 program to find length of a # Linked List using Tail recursion. # 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 using Tail Recursion.
def getCountRec( self , node, count = 0 ):
if ( not node): # Base case
return count
else :
return self .getCountRec(node. next , count + 1 )
# A wrapper over getCountRec()
def getCount( self ):
return self .getCountRec( self .head)
# Driver code if __name__ = = '__main__' :
llist = LinkedList()
llist.push( 1 )
llist.push( 3 )
llist.push( 1 )
llist.push( 2 )
llist.push( 1 )
# Function call
print ( 'Count of nodes is :' , llist.getCount())
# This code is contributed by garinesrija.
|
// 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 code
public static void Main(String[] args)
{
LinkedList llist = new LinkedList();
llist.push(1);
llist.push(3);
llist.push(1);
llist.push(2);
llist.push(1);
// Function call
Console.WriteLine( "Count of nodes is "
+ llist.getCount());
}
} // This code is contributed Abhijeet Kumar(abhijeet19403) |
<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> |
Count of nodes is 5
Time Complexity: O(N), As we are traversing the list only once.
Auxiliary Space: O(N), In worst case the depth of recursion call stack will be N.