Java Program To Check If A Linked List Of Strings Forms A Palindrome

Given a linked list handling string data, check to see whether data is palindrome or not? Examples:

Input: a -> bc -> d -> dcb -> a -> NULL
Output: True
String "abcddcba" is palindrome.

Input: a -> bc -> d -> ba -> NULL
Output: False
String "abcdba" is not palindrome. 

The idea is very simple. Construct a string out of given linked list and check if the constructed string is palindrome or not. 

Java

// Java Program to check if a given linked list
// of strings form a palindrome
import java.util.Scanner;

// Linked List node
class Node
{
    String data;
    Node next;

    Node(String d)
    {
        data = d;
        next = null;
    }
}

class LinkedList_Palindrome
{
    Node head;

    // A utility function to check if
    // str is palindrome or not
    boolean isPalidromeUtil(String str)
    {
        int length = str.length();

        // Match characters from beginning
        // and end.
        for (int i = 0; i < length / 2; i++)
            if (str.charAt(i) !=
                str.charAt(length - i - 1))
                return false;

        return true;
    }

    // Returns true if string formed by
    // linked list is palindrome
    boolean isPalindrome()
    {
        Node node = head;

        // Append all nodes to form a
        // string
        String str = "";
        while (node != null)
        {
            str = str.concat(node.data);
            node = node.next;
        }

        // Check if the formed string is
        // palindrome
        return isPalidromeUtil(str);
    }

    // Driver code
    public static void main(String[] args)
    {
        LinkedList_Palindrome list =
           new LinkedList_Palindrome();
        list.head = new Node("a");
        list.head.next = new Node("bc");
        list.head.next.next = new Node("d");
        list.head.next.next.next =
             new Node("dcb");
        list.head.next.next.next.next =
             new Node("a");
        System.out.println(list.isPalindrome());
    }
}
// This code is contributed by Amit Khandelwal

Output:

true

Time Complexity: O(n), where n is the number of nodes in the given linked list.
Auxiliary Space: O(m) where m is the length of the string formed by the linked list.

Please refer complete article on Check if a linked list of strings forms a palindrome for more details!