Recursive insertion and traversal linked list

We have discussed different methods of linked list insertion. How to recursively create a linked list?

Recursively inserting at the end: To create a Linked list using recursion follow these steps. Below steps insert a new node recursively at the end of linked list.  

C++

// Function to insert a new node at the
// end of linked list using recursion.
Node* insertEnd(Node* head, int data)
{
    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == NULL)
         return newNode(data);

    // If we have not reached end, keep traversing
    // recursively.
    else
        head->next = insertEnd(head->next, data);
    return head;
}

Java

// Function to insert a new node at the
// end of linked list using recursion.
static Node insertEnd(Node head, int data)
{

    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == null)
         return newNode(data);

    // If we have not reached end, keep traversing
    // recursively.
    else
        head.next = insertEnd(head.next, data);

    return head;
}

// This code is contributed by rutvik_56

Python3

# Function to insert a new node at the
# end of linked list using recursion.
def insertEnd(head, data):

    # If linked list is empty, create a
    # new node (Assuming newNode() allocates
    # a new node with given data)
    if (head == None):
        return newNode(data)

    # If we have not reached end,
    # keep traversing recursively.
    else:
        head.next = insertEnd(head.next, data)

    return head

# This code is contributed by divyeshrabadiya07

C#

// Function to insert a new node at the
// end of linked list using recursion.
static Node insertEnd(Node head, int data)
{

    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == null)
        return newNode(data);

    // If we have not reached end, keep traversing
    // recursively.
    else
        head.next = insertEnd(head.next, data);

    return head;
}

// This code is contributed by divyesh072019

Javascript

<script>

// Function to insert a new node at the
// end of linked list using recursion.
function insertEnd(head , data)
{

    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == null)
    {
        return newNode(data);
    }

    // If we have not reached end, keep traversing
    // recursively.
    else
    {
        head.next = insertEnd(head.next, data);
    }
    return head;
}

// This code is contributed by shubhamsingh10

</script>

Time Complexity: O(N) where N is the number of nodes in given linked list.

Auxiliary Space: O(N) due to recursion call stack.

Recursively traversing the list:
The idea is simple, we print current node and recur for remaining list.  

Implementation:

C++

void traverse(Node* head)
{
    if (head == NULL)
       return;

    // If head is not NULL, print current node
    // and recur for remaining list
    cout << head->data << " ";

    traverse(head->next);
}

Java

static void traverse(Node head)
{
    if (head == null)
    return;

    // If head is not null, print current node
    // and recur for remaining list
    System.out.print( head.data + " ");

    traverse(head.next);
}

// This code is contributed by SUBHAMSINGH10

Python3

def traverse(head):
    if (head == None):
        return

    # If head is not None, print current node
    # and recur for remaining list
    print(head.data, end = " ");
    traverse(head.next)

    # This code is contributed by Pratham76

C#

static void traverse(Node head)
{
    if (head == null)
    return;

    // If head is not null, print current node
    // and recur for remaining list
    Console.Write(head.data + " ");

    traverse(head.next);
}

Javascript

function traverse(head){
    if(head == null)
        return;

    // If head is not NULL, print current node
    // and recur for remaining list
    console.log(head.data + " ");
    traverse(head.next);
}

// This code is contributed by Yash Agarwal(yashagarwal2852002)

Complete Program: Below is complete program to demonstrate working of insert and traverse a linked list. 

C++

// Recursive C++ program to recursively insert
// a node and recursively print the list.
#include <bits/stdc++.h>
using namespace std;
struct Node {
    int data;
    Node* next;
};

// Allocates a new node with given data
Node *newNode(int data)
{
    Node *new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}

// Function to insert a new node at the
// end of linked list using recursion.
Node* insertEnd(Node* head, int data)
{
    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == NULL)
         return newNode(data);

    // If we have not reached end, keep traversing
    // recursively.
    else
        head->next = insertEnd(head->next, data);
    return head;
}

void traverse(Node* head)
{
    if (head == NULL)
       return;

    // If head is not NULL, print current node
    // and recur for remaining list
    cout << head->data << " ";

    traverse(head->next);
}

// Driver code
int main()
{
    Node* head = NULL;
    head = insertEnd(head, 6);
    head = insertEnd(head, 8);
    head = insertEnd(head, 10);
    head = insertEnd(head, 12);
    head = insertEnd(head, 14);
    traverse(head);
}

Java

// THIS CODE IS CONTRIBUTED BY KIRTI AGARWAL(KIRTIAGARWAL23121999)
// Recursive Java program to recursively insert
// a node and recursively print the list.
public class GFG {
    static class Node {
        int data;
        Node next;
    };

    // Allocates a new node with given data
    static Node newNode(int data){
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }

    // Function to insert a new node at the
    // end of linked list using recursion.
    static Node insertEnd(Node head, int data){
        // If linked list is empty, create a
        // new node (Assuming newNode() allocates
        // a new node with given data)
        if (head == null)
            return newNode(data);

        // If we have not reached end, keep traversing
        // recursively.
        else
            head.next = insertEnd(head.next, data);
        return head;
    }

    static void traverse(Node head){
        if (head == null)
            return;

        // If head is not null, print current node
        // and recur for remaining list
        System.out.print(head.data + " ");
        traverse(head.next);
    }

    // Driver code
    public static void main(String args[]){
        Node head = null;
        head = insertEnd(head, 6);
        head = insertEnd(head, 8);
        head = insertEnd(head, 10);
        head = insertEnd(head, 12);
        head = insertEnd(head, 14);
        traverse(head);
    }
}

Python3

# Recursive Python3 program to
# recursively insert a node and
# recursively print the list.
import math

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# Allocates a new node with given data
def newNode(data):
    new_node = Node(data)
    new_node.data = data
    new_node.next = None
    return new_node

# Function to insert a new node at the
# end of linked list using recursion.
def insertEnd(head, data):

    # If linked list is empty, create a
    # new node (Assuming newNode() allocates
    # a new node with given data)
    if (head == None):
        return newNode(data)

    # If we have not reached end,
    # keep traversing recursively.
    else:
        head.next = insertEnd(head.next, data)
    return head

def traverse(head):
    if (head == None):
        return

    # If head is not None, print current node
    # and recur for remaining list
    print(head.data, end = " ");
    traverse(head.next)

# Driver code
if __name__=='__main__':
    head = None
    head = insertEnd(head, 6)
    head = insertEnd(head, 8)
    head = insertEnd(head, 10)
    head = insertEnd(head, 12)
    head = insertEnd(head, 14)
    traverse(head)

# This code is contributed by sapna singh

C#

// Recursive C# program to recursively insert
// a node and recursively print the list.
using System;

class GFG
{

public class Node
{
    public int data;
    public Node next;
};

// Allocates a new node with given data
static Node newNode(int data)
{
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = null;
    return new_node;
}

// Function to insert a new node at the
// end of linked list using recursion.
static Node insertEnd(Node head, int data)
{
    // If linked list is empty, create a
    // new node (Assuming newNode() allocates
    // a new node with given data)
    if (head == null)
        return newNode(data);

    // If we have not reached end, keep traversing
    // recursively.
    else
        head.next = insertEnd(head.next, data);
    return head;
}

static void traverse(Node head)
{
    if (head == null)
    return;

    // If head is not null, print current node
    // and recur for remaining list
    Console.Write(head.data + " ");

    traverse(head.next);
}

// Driver code
public static void Main(String []args)
{
    Node head = null;
    head = insertEnd(head, 6);
    head = insertEnd(head, 8);
    head = insertEnd(head, 10);
    head = insertEnd(head, 12);
    head = insertEnd(head, 14);
    traverse(head);
}
}

// This code is contributed by 29AjayKumar

Javascript

<script>
    // Recursive Javascript program to recursively insert
    // a node and recursively print the list.

    class Node
    {
        constructor(data) {
           this.next = null;
           this.data = data;
        }
    }

    // Allocates a new node with given data
    function newNode(data)
    {
        let new_node = new Node(data);
        return new_node;
    }

    // Function to insert a new node at the
    // end of linked list using recursion.
    function insertEnd(head, data)
    {
        // If linked list is empty, create a
        // new node (Assuming newNode() allocates
        // a new node with given data)
        if (head == null)
            return newNode(data);

        // If we have not reached end, keep traversing
        // recursively.
        else
            head.next = insertEnd(head.next, data);
        return head;
    }

    function traverse(head)
    {
        if (head == null)
            return;

        // If head is not null, print current node
        // and recur for remaining list
        document.write(head.data + " ");

        traverse(head.next);
    }

    let head = null;
    head = insertEnd(head, 6);
    head = insertEnd(head, 8);
    head = insertEnd(head, 10);
    head = insertEnd(head, 12);
    head = insertEnd(head, 14);
    traverse(head);

// This code is contributed by mukesh07.
</script>

Output

6 8 10 12 14 

Time Complexity: O(N), to traverse the linked list of size N.
Auxiliary Space: O(N), for recursion call stack

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