# Java program to check whether linked list is palindrome or not

## Java program to check whether linked list is palindrome or not

Java program to check whether the linked list is palindrome or not. In this program, we have to check whether the given linked list is palindromic or not. A palindrome is a list which has the property of reversing itself. To check whether a number is palindrome or not, we traverse the list and check if any element from the starting half doesn’t  match with the ending half of a list then we say it’s not a palindrome number otherwise it is palindrome. ## Implementation for Checking a list is palindrome or not :-

• First get the middle node of the given Linked List let take Consideration for both the odd and even cases.
• Then, we will reverse the second half of the Linked List.
• We will compare the second half with the first half if both the halves are identical then the linked list is a palindrome.
• Reconstruct the actual given Linked List by again reversing the second half and attaching it back to the first half.

### Example :

After reversing it will stay as it is

1–>2–>3–>2–>1   (true) (It is a palindrome list) ## Code in JAVA Programming Language

Run
```import java.util.*;

public class Main
{

public static void main (String[]args) throws Exception
{

ll.display ();

System.out.println (ll.isPalindrome ());

}

}

{
private class Node
{
int data;
Node next;

// Node constructor
// There are two fields in the node- data and address of next node
public Node (int data, Node next)
{
this.data = data;
this.next = next;
}
}

private Node tail;
private int size;

{
this.tail = null;
this.size = 0;

}

// Function to find the size of linked list
public int size ()
{
return this.size;
}

// Function to check whether linked list is empty or not
public boolean isEmpty ()
{
return this.size () == 0;
}

// Function to traverse and print the linked list
public void display ()
{
while (temp != null)
{
System.out.print (temp.data + "  ");

temp = temp.next;
}
System.out.println ("END");
}

{
// Create a temp node which points to head
Node temp = new Node (item, head);

// If linked list is empty, temp is the head and tail node both
if (this.size == 0)
{
}

// else set the head such that it now points to temp node
else
{

}

this.size++;
}

public boolean isPalindrome ()
{
HeapMover start = new HeapMover ();

}

//Function to check whether linked list is palindrome or not
private boolean isPalindrome (HeapMover start, Node end, int floor)
{

//Base case is when we reach end of linked list
if (end == null)
{
return true;
}

//Recursive calls
boolean rv = this.isPalindrome (start, end.next, floor + 1);

//If any recursive call results in false then return false
if (rv == false)
{
return false;
}

//Till floor is greater than 1/2 * size of linked list
if (floor >= this.size () / 2)
{

//If data of start node and end node is not same then it is not palindrome
if (start.node.data != end.data)
{
return false;

}

//Change start node so that it now points to the next node
else
{
start.node = start.node.next;
return true;
}

}
return rv;

}

//Class to keep a node in the heap
private class HeapMover
{
Node node;
}

}```
```Output:
10  20  30  40  40  30  20  10  END
true
```

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