Regarding finding the middle element of linked list

Question

I am following the below approach to calculate the middle element from the linked list , but I want is there any built in method or any other approach which can also find the same easily , the approach that I am following is shown bellow..

import test.LinkedList.Node;
public class LinkedListTest {


    public static void main(String args[]) {
        //creating LinkedList with 5 elements including head
      LinkedList linkedList = new LinkedList();
      LinkedList.Node head = linkedList.head();
      linkedList.add( new LinkedList.Node("1"));
      linkedList.add( new LinkedList.Node("2"));
      linkedList.add( new LinkedList.Node("3"));
      linkedList.add( new LinkedList.Node("4"));

      //finding middle element of LinkedList in single pass
      LinkedList.Node current = head;
      int length = 0;
      LinkedList.Node middle = head;

      while(current.next() != null){
          length++;
          if(length%2 ==0){
              middle = middle.next();
          }
          current = current.next();
      }

      if(length%2 == 1){
          middle = middle.next();
      }

      System.out.println("length of LinkedList: " + length);
      System.out.println("middle element of LinkedList : " + middle);

    } 

}

class LinkedList{
    private Node head;
    private Node tail;

    public LinkedList(){
        this.head = new Node("head");
        tail = head;
    }

    public Node head(){
        return head;
    }

    public void add(Node node){
        tail.next = node;
        tail = node;
    }

    public static class Node{
        private Node next;
        private String data;

        public Node(String data){
            this.data = data;
        }

        public String data() {
            return data;
        }

        public void setData(String data) {
            this.data = data;
        }

        public Node next() {
            return next;
        }

        public void setNext(Node next) {
            this.next = next;
        }

        public String toString(){
            return this.data;
        }
    }
}

Output:-

length of LinkedList: 4
middle element of LinkedList : 2

Answer 1

The basic algorithm would be

• Take two pointers

• Make both pointing to first node

• Increment first with two nodes and second with one, at a time.

• Loop until the 1st loop reaches the end. At this point, the 2nd will be at the middle.

Example:-

while ( p2.next != null ) {
    p2 = p2.next;
    if (p2.next != null) {
        p2 = p2.next;
        p1 = p1.next;
    }
}

It will definitely work in odd case, for even case you need to check one more condition if first point is allowed to move next but not next to next then both pointers will be at middle you need to decide which to take as middle.

Answer 2

I would recommend using the Java built in

LinkedList<Object e>

It gives you all the functionality you need like getting the length: list.size(), and the middle object:

list.get((list.size())/2);