Make a loop at k-th position in a linked list

Last Updated : 17 Jan, 2023

Given a linked list and a position k. Make a loop at k-th position

Examples:

Input : Given linked list

Output : Modified linked list

Algorithm:

Traverse the first linked list till k-th point
Make backup of the k-th node
Traverse the linked list till end
Attach the last node with k-th node

Implementation:

C++

// CPP program for making loop at k-th index
// of given linked list
#include <bits/stdc++.h>
using namespace std;

/* Link list node */
struct Node {
    int data;
    struct Node* next;
};

/* Function to make loop at k-th elements of
linked list */
void makeloop(struct Node** head_ref, int k)
{
    // traverse the linked list until loop
    // point not found
    struct Node* temp = *head_ref;
    int count = 1;
    while (count < k) {
        temp = temp->next;
        count++;
    }

    // backup the joint point 
    struct Node* joint_point = temp; 

    // traverse remaining nodes
    while (temp->next != NULL) 
        temp = temp->next;

    // joint the last node to k-th element
    temp->next = joint_point;
}

/* Function to push a node */
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node =
        (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

/* Function to print linked list */
void printList(struct Node* head, int total_nodes)
{
    struct Node* curr = head;
    int count = 0;
    while (count < total_nodes) {
        count++;
        cout << curr->data << " ";
        curr = curr->next;
    }
}

int countNodes(Node *ptr)
{
    int count = 0;
    while (ptr != NULL)
    {
        ptr = ptr->next;
        count++;
    }
    return count;
}

/* Driver program to test above function*/
int main()
{
    // Create a linked list 1->2->3->4->5->6->7
    struct Node* head = NULL;
    push(&head, 7);
    push(&head, 6);
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);

    // k should be less than the
    // numbers of nodes
    int k = 4;
    int total_nodes = countNodes(head);

    cout << "\nGiven list\n";
    printList(head, total_nodes);

    makeloop(&head, k);

    cout << "\nModified list\n";
    printList(head, total_nodes);
    return 0;
}

Java

// Java program for making loop at k-th index 
// of given linked list 
class GFG
{
    
// Link list node /
static class Node
{ 
    int data; 
    Node next; 
} 

// Function to make loop at k-th elements of 
//linked list /
static Node makeloop( Node head_ref, int k) 
{ 
    // traverse the linked list until loop 
    // point not found 
    Node temp = head_ref; 
    int count = 1; 
    while (count < k)
    { 
        temp = temp.next; 
        count++; 
    } 

    // backup the joint point 
    Node joint_point = temp; 

    // traverse remaining nodes 
    while (temp.next != null) 
        temp = temp.next; 

    // joint the last node to k-th element 
    temp.next = joint_point; 
    return head_ref;
} 

// Function to push a node /
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;
} 

// Function to print linked list /
static void printList( Node head, int total_nodes) 
{ 
    Node curr = head; 
    int count = 0; 
    while (count < total_nodes)
    { 
        count++; 
        System.out.print(curr.data + " "); 
        curr = curr.next; 
    } 
} 

static int countNodes(Node ptr) 
{ 
    int count = 0; 
    while (ptr != null) 
    { 
        ptr = ptr.next; 
        count++; 
    } 
    return count; 
} 

// Driver code
public static void main(String args[])
{ 
    // Create a linked list 1.2.3.4.5.6.7 
    Node head = null; 
    head = push(head, 7); 
    head = push(head, 6); 
    head = push(head, 5); 
    head = push(head, 4); 
    head = push(head, 3); 
    head = push(head, 2); 
    head = push(head, 1); 

    // k should be less than the 
    // numbers of nodes 
    int k = 4; 
    int total_nodes = countNodes(head); 

    System.out.print("\nGiven list\n"); 
    printList(head, total_nodes); 

    head = makeloop(head, k); 

    System.out.print( "\nModified list\n"); 
    printList(head, total_nodes); 
}
} 

// This code is contributed by Arnab Kundu

Python3

# Python3 program for making loop at k-th index
# of given linked list
import math

# Link list node 
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None

# Function to make loop at k-th elements of
#linked list 
def makeloop(head_ref, k):
    
    # traverse the linked list until loop
    # point not found
    temp = head_ref
    count = 1
    while (count < k):
        temp = temp.next
        count = count + 1

    # backup the joint point 
    joint_point = temp 

    # traverse remaining nodes
    while (temp.next != None): 
        temp = temp.next

    # joint the last node to k-th element
    temp.next = joint_point
    return head_ref

# Function to push a node 
def push(head_ref, new_data):
    new_node = Node(new_data)
    new_node.data = new_data
    new_node.next = head_ref
    head_ref = new_node
    return head_ref

# Function to print linked list 
def printList( head,total_nodes):
    curr = head
    count = 0
    while (count < total_nodes):
        count = count + 1
        print(curr.data, end = " ")
        curr = curr.next
    
def countNodes(ptr):
    count = 0
    while (ptr != None):
        ptr = ptr.next
        count = count + 1
    
    return count

# Driver Code
if __name__=='__main__':
    
    # Create a linked list 1.2.3.4.5.6.7
    head = None
    head = push(head, 7)
    head = push(head, 6)
    head = push(head, 5)
    head = push(head, 4)
    head = push(head, 3)
    head = push(head, 2)
    head = push(head, 1)

    # k should be less than the
    # numbers of nodes
    k = 4
    total_nodes = countNodes(head)

    print("Given list")
    printList(head, total_nodes)

    makeloop(head, k)

    print("\nModified list")
    printList(head, total_nodes)
    
# This code is contributed by Srathore

// C# program for making loop at k-th index 
// of given linked list 
using System;

class GFG
{
    
// Link list node /
public class Node
{ 
    public int data; 
    public Node next; 
} 

// Function to make loop at k-th elements of 
//linked list /
static Node makeloop( Node head_ref, int k) 
{ 
    // traverse the linked list until loop 
    // point not found 
    Node temp = head_ref; 
    int count = 1; 
    while (count < k)
    { 
        temp = temp.next; 
        count++; 
    } 

    // backup the joint point 
    Node joint_point = temp; 

    // traverse remaining nodes 
    while (temp.next != null) 
        temp = temp.next; 

    // joint the last node to k-th element 
    temp.next = joint_point; 
    return head_ref;
} 

// Function to push a node /
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;
} 

// Function to print linked list /
static void printList( Node head, int total_nodes) 
{ 
    Node curr = head; 
    int count = 0; 
    while (count < total_nodes)
    { 
        count++; 
        Console.Write(curr.data + " "); 
        curr = curr.next; 
    } 
} 

static int countNodes(Node ptr) 
{ 
    int count = 0; 
    while (ptr != null) 
    { 
        ptr = ptr.next; 
        count++; 
    } 
    return count; 
} 

// Driver code
public static void Main(String []args)
{ 
    // Create a linked list 1.2.3.4.5.6.7 
    Node head = null; 
    head = push(head, 7); 
    head = push(head, 6); 
    head = push(head, 5); 
    head = push(head, 4); 
    head = push(head, 3); 
    head = push(head, 2); 
    head = push(head, 1); 

    // k should be less than the 
    // numbers of nodes 
    int k = 4; 
    int total_nodes = countNodes(head); 

    Console.Write("\nGiven list\n"); 
    printList(head, total_nodes); 

    head = makeloop(head, k); 

    Console.Write( "\nModified list\n"); 
    printList(head, total_nodes); 
}
}

// This code contributed by Rajput-Ji

JavaScript

<script>
// javascript program for making loop at k-th index 
// of given linked list     
// Link list node /
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}

    // Function to make loop at k-th elements of
    // linked list /
    function makeloop(head_ref , k) {
        // traverse the linked list until loop
        // point not found
var temp = head_ref;
        var count = 1;
        while (count < k) {
            temp = temp.next;
            count++;
        }

        // backup the joint point
var joint_point = temp;

        // traverse remaining nodes
        while (temp.next != null)
            temp = temp.next;

        // joint the last node to k-th element
        temp.next = joint_point;
        return head_ref;
    }

    // Function to push a node /
    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;
    }

    // Function to print linked list /
    function printList(head , total_nodes) {
var curr = head;
        var count = 0;
        while (count < total_nodes) {
            count++;
            document.write(curr.data + " ");
            curr = curr.next;
        }
    }

    function countNodes(ptr) {
        var count = 0;
        while (ptr != null) {
            ptr = ptr.next;
            count++;
        }
        return count;
    }

    // Driver code
    
        // Create a linked list 1.2.3.4.5.6.7
var head = null;
        head = push(head, 7);
        head = push(head, 6);
        head = push(head, 5);
        head = push(head, 4);
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 1);

        // k should be less than the
        // numbers of nodes
        var k = 4;
        var total_nodes = countNodes(head);

        document.write("<br/>Given list<br/>");
        printList(head, total_nodes);

        head = makeloop(head, k);

        document.write("<br/>Modified list<br/>");
        printList(head, total_nodes);

// This code contributed by umadevi9616
</script>

Output

Given list
1 2 3 4 5 6 7 
Modified list
1 2 3 4 5 6 7

Time Complexity: O(N), where N is the number of nodes in the given linked list.
Auxiliary Space: O(1)

Analysis of Algorithms

Shahnawaz_Ali

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