Recursive function to delete k-th node from linked list

Given a singly linked list, delete a node at the kth position without using the loop.

Examples:

Input : list = 9->8->3->5->2->1 
          k = 4
Output : 9->8->3->2->1 

Input  : list = 0->0->1->6->2->3 
            k = 3
Output : 0->0->6->2->3  

We recursively reduce the value of k. When k reaches 1, we delete the current node and return the next current node as a new node. When the function returns, we link the returned node to the next previous node. 

Implementation:

C++

// Recursive CPP program to delete k-th node
// of a linked list
#include <bits/stdc++.h>
using namespace std;

struct Node {
    int data;
    struct Node* next;
};

// Deletes k-th node and returns new header.
Node* deleteNode(Node* start, int k)
{
    // If invalid k
    if (k < 1)
       return start;

    // If linked list is empty
    if (start == NULL)
       return NULL;

    // Base case (start needs to be deleted)
    if (k == 1)
    {
        Node *res = start->next;
        delete(start);
        return res;
    }

    start->next = deleteNode(start->next, k-1);
    return start;
}

/* Utility function to insert a node at the beginning */
void push(struct Node **head_ref, int new_data)
{
    struct Node *new_node = new Node;
    new_node->data = new_data;
    new_node->next = *head_ref;
    *head_ref = new_node;
}

/* Utility function to print a linked list */
void printList(struct Node *head)
{
    while (head!=NULL)
    {
        cout << head->data << " ";
        head = head->next;
    }
    printf("\n");
}

/* Driver program to test above functions */
int main()
{
    struct Node *head = NULL;

    /* Create following linked list
      12->15->10->11->5->6->2->3 */
    push(&head,3);
    push(&head,2);
    push(&head,6);
    push(&head,5);
    push(&head,11);
    push(&head,10);
    push(&head,15);
    push(&head,12);

    int k = 3;
    head = deleteNode(head, k);

    printf("\nModified Linked List: ");
    printList(head);

    return 0;
}

Java

// Recursive Java program to delete k-th node
// of a linked list
class GFG
{

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

// Deletes k-th node and returns new header.
static Node deleteNode(Node start, int k)
{
    // If invalid k
    if (k < 1)
    return start;

    // If linked list is empty
    if (start == null)
    return null;

    // Base case (start needs to be deleted)
    if (k == 1)
    {
        Node res = start.next;
        return res;
    }

    start.next = deleteNode(start.next, k-1);
    return start;
}

// Utility function to insert a node at the beginning /
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;
}

// Utility function to print a linked list /
static void printList( Node head)
{
    while (head!=null)
    {
        System.out.print(head.data + " ");
        head = head.next;
    }
    System.out.printf("\n");
}

// Driver program to test above functions /
public static void main(String args[])
{
    Node head = null;

    // Create following linked list
    //12.15.10.11.5.6.2.3 /
    head=push(head,3);
    head=push(head,2);
    head=push(head,6);
    head=push(head,5);
    head=push(head,11);
    head=push(head,10);
    head=push(head,15);
    head=push(head,12);

    int k = 3;
    head = deleteNode(head, k);

    System.out.printf("\nModified Linked List: ");
    printList(head);
}
}

// This code is contributed by Arnab Kundu

Python3

# Recursive Java program to delete k-th node
# of a linked list
class Node(object):
    def __init__(self, d):
        self.data = d
        self.next = None

# Deletes k-th node and returns new header.
def deleteNode(start, k) :

    # If invalid k
    if (k < 1) :
        return start

    # If linked list is empty
    if (start == None):
        return None

    # Base case (start needs to be deleted)
    if (k == 1) :

        res = start.next
        return res

    start.next = deleteNode(start.next, k - 1)
    return start

# Utility function to insert a node
# at the beginning
def push(head_ref, new_data) :

    new_node = Node(0)
    new_node.data = new_data
    new_node.next = head_ref
    head_ref = new_node
    return head_ref

# Utility function to print a linked list
def printList( head) :

    while (head != None):

        print(head.data, end = " ")
        head = head.next

    print("\n")

# Driver Code
head = None

# Create following linked list
# 12.15.10.11.5.6.2.3 /
head = push(head, 3)
head = push(head, 2)
head = push(head, 6)
head = push(head, 5)
head = push(head, 11)
head = push(head, 10)
head = push(head, 15)
head = push(head, 12)

k = 3
head = deleteNode(head, k)

print("Modified Linked List: ", end = "")
printList(head)

# This code is contributed by Arnab Kundu

C#

// Recursive C# program to delete k-th node
// of a linked list
using System;

class GFG
{

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

    // Deletes k-th node and returns new header.
    static Node deleteNode(Node start, int k)
    {
        // If invalid k
        if (k < 1)
        return start;

        // If linked list is empty
        if (start == null)
        return null;

        // Base case (start needs to be deleted)
        if (k == 1)
        {
            Node res = start.next;
            return res;
        }

        start.next = deleteNode(start.next, k-1);
        return start;
    }

    // Utility function to insert a node at the beginning /
    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;
    }

    // Utility function to print a linked list /
    static void printList( Node head)
    {
        while (head != null)
        {
            Console.Write(head.data + " ");
            head = head.next;
        }
        Console.Write("\n");
    }

    // Driver program to test above functions /
    public static void Main(String []args)
    {
        Node head = null;

        // Create following linked list
        //12.15.10.11.5.6.2.3 /
        head=push(head,3);
        head=push(head,2);
        head=push(head,6);
        head=push(head,5);
        head=push(head,11);
        head=push(head,10);
        head=push(head,15);
        head=push(head,12);

        int k = 3;
        head = deleteNode(head, k);

        Console.Write("\nModified Linked List: ");
        printList(head);
    }
}

/* This code contributed by PrinciRaj1992 */

Javascript

<script>
// Recursive javascript program to delete k-th node
// of a linked list
    class Node {
        constructor(val) {
            this.data = val;
            this.next = null;
        }
    }

    // Deletes k-th node and returns new header.
    function deleteNode(start , k) {
        // If invalid k
        if (k < 1)
            return start;

        // If linked list is empty
        if (start == null)
            return null;

        // Base case (start needs to be deleted)
        if (k == 1) {
            var res = start.next;
            return res;
        }

        start.next = deleteNode(start.next, k - 1);
        return start;
    }

    // Utility function to insert a node at the beginning /
    function push(head_ref , new_data) {
        var new_node = new Node();
        new_node.data = new_data;
        new_node.next = head_ref;
        head_ref = new_node;
        return head_ref;
    }

    // Utility function to print a linked list /
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
        document.write("\n");
    }

    // Driver program to test above functions /

        var head = null;

        // Create following linked list
        // 12.15.10.11.5.6.2.3 /
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 6);
        head = push(head, 5);
        head = push(head, 11);
        head = push(head, 10);
        head = push(head, 15);
        head = push(head, 12);

        var k = 3;
        head = deleteNode(head, k);

        document.write("\nModified Linked List: ");
        printList(head);

// This code is contributed by todaysgaurav
</script>

Output

Modified Linked List: 12 15 11 5 6 2 3 

Time Complexity:  O(n)
Auxiliary Space: O(n)

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