Java Program to Get the middle element of LinkedList in a single iteration

In this example, we will learn to get the middle element of the linked list in a single iteration in Java.

To understand this example, make sure you first visit the following tutorials,

Example 1: Get the middle element of LinkedList in a single search

``````class LinkedList {

// create an object of Node class

// static inner class
static class Node {
int value;

// connect each node to next node
Node next;

Node(int d) {
value = d;
next = null;
}
}

public static void main(String[] args) {

// create an object of LinkedList

// assign values to each linked list node
Node second = new Node(2);
Node third = new Node(3);

// connect each node of linked list to next node
second.next = third;

while (pointer != null) {
System.out.print(pointer.value + " ");
pointer = pointer.next;
}

// Find the middle element

while (ptr1.next != null) {

// increase the ptr1 by 2 and ptr2 by 1
// if ptr1 points to last element
// ptr2 will points to middle element
ptr1 = ptr1.next;
if(ptr1.next !=null) {
ptr1 = ptr1.next;
ptr2 = ptr2.next;
}
}

System.out.println("\nMiddle Element: " + ptr2.value);

}
}``````

Output

```LinkedList: 1 2 3
Middle Element: 2```

In the above example, we have implemented the linked list data structure in Java. We then find the middle element of the linked list in a single loop. Notice the code,

``````    while (ptr1.next != null) {

// increase the ptr1 by 2 and ptr2 by 1
// if ptr1 points to last element
// ptr2 will points to middle element
ptr1 = ptr1.next;
if(ptr1.next !=null) {
ptr1 = ptr1.next;
ptr2 = ptr2.next;
}
}``````

Here, we have two variables ptr1 and ptr2. We use these variables to iterate through the linked list.

In each iteration, the ptr1 will access the two nodes and the ptr2 will access the single node of the linked list.

Now, when the ptr1 reaches the end of the linked list, the ptr2 will be in the middle. In this way, we are able to get the middle of linked list in a single iteration.

Example 2: Get the middle element of LinkedList using the LinkedList class

``````import java.util.LinkedList;

class Main {
public static void main(String[] args){

// access middle element
String middle = animals.get(animals.size()/2);
System.out.println("Middle Element: " + middle);
}
}``````

Output

```LinkedList: [Cat, Dog, Horse]
Middle Element: Dog```

In the above example, we have used the `LinkedList` class to implement the linked list data structure. Notice the expression,

``animals.get(animals.size()/2)``
• size()/2 - returns the position of middle element
• get() - returns the element at the middle position