Get Middle Element of LinkedList in a Single Iteration

In this article, we will understand how to get the middle element of linkedList in a single iteration. The java.util.LinkedList class operations perform we can expect for a doubly-linked list. Operations that index into the list will traverse the list from the beginning or the end, whichever is closer to the specified index.

Below is a demonstration of the same −

Suppose our input is −

Input linked list: 100 200 330

The desired output would be −

The middle element of the list is: 200

Algorithm

Step 1 - START
Step 2 - Declare a LinkedList namely input_list. Declare five node objects namely head, first_node, second_node, pointer_1, pointer_2.
Step 3 - Define the values.
Step 4 - Using a while loop, iterate over the linked list, get the middle element by traversing the list using pointer_1 and pointer_2 until pointer_1.next is not null.
Step 5 - Display the pointer_2 value as result.
Step 6 - Stop

Example 1

Here, we bind all the operations together under the ‘main’ function.

public class LinkedList {
   Node head;
   static class Node {
      int value;
      Node next;
      Node(int d) {
         value = d;
         next = null;
      }
   }
   public static void main(String[] args) {
      LinkedList input_list = new LinkedList();
      input_list.head = new Node(100);
      Node second_node = new Node(200);
      Node third_node = new Node(330);
      input_list.head.next = second_node;
      second_node.next = third_node;
      Node current_node = input_list.head;
      System.out.print("The linked list is defined as: " );
      while (current_node != null) {
         System.out.print(current_node.value + " ");
         current_node = current_node.next;
      }
      Node pointer_1 = input_list.head;
      Node pointer_2 = input_list.head;
      while (pointer_1.next != null) {
         pointer_1 = pointer_1.next;
         if(pointer_1.next !=null) {
            pointer_1 = pointer_1.next;
            pointer_2 = pointer_2.next;
         }
      }
      System.out.println("\nThe middle element of the list is: " + pointer_2.value);
   }
}

Output

The linked list is defined as: 100 200 330
The middle element of the list is: 200

Example 2

Here, we encapsulate the operations into functions exhibiting object oriented programming.

public class LinkedList {
   Node head;
   static class Node {
      int value;
      Node next;
      Node(int d) {
         value = d;
         next = null;
      }
   }
   static void get_middle_item(LinkedList input_list){
      Node pointer_1 = input_list.head;
      Node pointer_2 = input_list.head;
      while (pointer_1.next != null) {
         pointer_1 = pointer_1.next;
         if(pointer_1.next !=null) {
            pointer_1 = pointer_1.next;
            pointer_2 = pointer_2.next;
         }
      }
      System.out.println("\nThe middle element of the list is: " + pointer_2.value);
   }
   public static void main(String[] args) {
      LinkedList input_list = new LinkedList();
      input_list.head = new Node(100);
      Node second_node = new Node(200);
      Node third_node = new Node(330);
      input_list.head.next = second_node;
      second_node.next = third_node;
      Node current_node = input_list.head;
      System.out.print("The linked list is defined as: " );
      while (current_node != null) {
         System.out.print(current_node.value + " ");
         current_node = current_node.next;
      }
      get_middle_item(input_list);
   }
}

Output

The linked list is defined as: 100 200 330
The middle element of the list is: 200