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Java program to find middle of a linked list

How to find middle of a linked list?

In here we are learning about a Java program to find the middle of a linked list. To find a middle of a linked , before that we should know that the number of link nodes are even or odd . If it’s odd then we have to take two pointer’s p1 and p2 as shown in the diagram p1 will move forward by one node and p2 will move forward two nodes. When p2 reaches the end of a linked list at that time p1 will be at the middle node of the linked list.

program to find middle of a linked list

Insertion in the middle of linked list in Java

Java program to find the middle of a linked list, (even case) When given number of link nodes are even we will follow the same fashion ad we are doing in odd case but over here we will divide the number of link nodes by 2 so as to get the middle node of a linked list

Example:

input: 1–>2–>3–>4–>5

output

3

The middle of a given linked list is 3

Find middle of a linked list

Algorithm.

Step 1– Start

Step 2– Initialize a class

Step 3– Give input

Step 4– Node constructor

Step 5– Linked list constructor

Step 6– Add a function to find the size of a linked list. // return this.size

Step 7 – Check whether the linked list is empty or not // return this.size () == 0

Step 8– run a loop for traversing the pointer and then print the linked list

Step 9– Add a node in the beginning.

Step 10– Create a temp node which points towards the head

Step 11– Linked list is empty, then head and tail both is temp

Step 12– add a function for finding the mid node.

Step 13– Take two pointers p1 and p2

Step 14– Move p1 by one node and p2 by two nodes

Step 15– When p2 reaches the end of a linked list, p1 will point to the middle node.

Step 16– End.

Java Program to find middle of a Linked List

Run
import java.lang.*;

class LinkedList
{
  Node head;
  // not using parameterized constructor would by default
  // force head instance to become null
  // Node head = null;  // can also do this, but not required

  // Node Class
  class Node
  {
    int data;
    Node next;

      Node (int x)		// parameterized constructor
    {
      data = x;
      next = null;
    }
  }
  public Node insert (int data)
  {
    // Creating newNode memory & assigning data value
    Node newNode = new Node (data);
    // assigning this newNode's next as current head node
    newNode.next = head;

    // re-assigning head to this newNode
    head = newNode;

    return head;
  }


  public void display ()
  {
    Node node = head;
    //as linked list will end when Node reaches Null
    while (node != null)
      {
	System.out.print (node.data + " ");
	node = node.next;
      }
    System.out.println ();
  }

  public int mid ()
  {
    return this.midNode ().data;
  }

  //Function to find the mid node
  private Node midNode ()
  {

//Take two pointers p1 and p2
    Node p1 = this.head;
    Node p2 = this.head;

//Move p1 by one node and p2 by two nodes
    while (p2.next != null && p2.next.next != null)
      {
	p1 = p1.next;
	p2 = p2.next.next;
      }

//When p2 reaches the end, p1 will point to the mid node
    return p1;

  }



}

class Main
{
  public static void main (String args[])
  {
    LinkedList ll = new LinkedList ();

      ll.insert (6);
      ll.insert (5);
      ll.insert (3);
      ll.insert (4);
      ll.insert (2);


      ll.display ();

      System.out.println ("Middle of the linked list is :- ");
      System.out.println (ll.mid ());


  }
}
Output: 

2 4 3 5 6 
Middle of the linked list is :- 
3

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One comment on “Java program to find middle of a linked list”


  • Mayank Tambe

    public node findmid(){
    int mid=(size()%2)+(size()/2);

    node temp=head;
    while(mid–>1){
    temp=temp.next;
    d=temp.data;
    }
    return temp;
    }