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How to detect a loop in linked list. If linked list has loop, find the start node for the loop.

Golu Rawat answered on August 24, 2022 Popularity 9/10 Helpfulness 1/10

answer How to detect a loop in linked list. If linked list has loop, find the start node for the loop.

How to detect a loop in linked list. If linked list has loop, find the start node for the loop.

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// Java program to detect  and remove loop in a linked list
import java.util.*;
  
public class LinkedList {
  
    static Node head; // head of list
  
    /* Linked list Node*/
    static class Node {
        int data;
        Node next;
        Node(int d)
        {
            data = d;
            next = null;
        }
    }
  
    /* Inserts a new Node at front of the list. */
    static 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;
    }
  
    // Function to print the linked list
    void printList(Node node)
    {
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
    }
  
    // Returns true if the loop is removed from the linked
    // list else returns false.
    static boolean removeLoop(Node h)
    {
        HashSet<Node> s = new HashSet<Node>();
        Node prev = null;
        while (h != null) {
            // If we have already has this node
            // in hashmap it means their is a cycle and we
            // need to remove this cycle so set the next of
            // the previous pointer with null.
  
            if (s.contains(h)) {
                prev.next = null;
                return true;
            }
  
            // If we are seeing the node for
            // the first time, insert it in hash
            else {
                s.add(h);
                prev = h;
                h = h.next;
            }
        }
  
        return false;
    }
  
    /* Driver program to test above function */
    public static void main(String[] args)
    {
        LinkedList llist = new LinkedList();
  
        llist.push(20);
        llist.push(4);
        llist.push(15);
        llist.push(10);
  
        /*Create loop for testing */
        llist.head.next.next.next.next = llist.head;
  
        if (removeLoop(head)) {
            System.out.println("Linked List after removing loop");
            llist.printList(head);
        }
        else
            System.out.println("No Loop found");
    }
}
  
// This code is contributed by Animesh Nag.

Popularity 9/10 Helpfulness 1/10 Language java

Source: www.geeksforgeeks.org

Tags: detect find java linked-list

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Contributed on Aug 24 2022

Golu Rawat

0 Answers Avg Quality 2/10

How to detect a loop in linked list. If linked list has loop, find the start node for the loop.

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