Resolving Head Modification Issues in LinkedList Palindrome Checking with Java

Discover how to avoid modifying the `head` of your LinkedList when checking for palindromes in Java. Follow this detailed guide for step-by-step solutions.
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This video is based on the question https://stackoverflow.com/q/77260866/ asked by the user 'Aditya Raj' ( https://stackoverflow.com/u/21905702/ ) and on the answer https://stackoverflow.com/a/77260979/ provided by the user 'chashikajw' ( https://stackoverflow.com/u/6213626/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Prevent Head Modification in LinkedList Palindrome Checking

When working with linked lists in Java, you might encounter an issue where the head of the list gets modified while performing operations such as checking for palindromes. This can be quite frustrating, especially when your code works seemingly well but doesn't yield the correct results. In this article, we will explore the reason behind this problem and provide a detailed solution that ensures your head remains intact.

Understanding the Problem

In your attempt to check if a linked list is a palindrome, you noticed that the head was modified and ended up pointing to the end of the list. The code you wrote effectively reversed the linked list instead of merely checking the values, causing the original list to be lost.

What is a Palindrome Linked List?

A palindrome linked list is defined as a sequence of nodes where the values read the same backward as forward. For example, the linked list formed by the values [1, 2, 2, 1] is a palindrome.

Why Does the Issue Occur?

The problem arises because when you reverse a linked list to check for a palindrome, the reference in your head gets overwritten. This effectively truncates the list from its logical beginning, making future operations on the original list impossible.

The Solution

To solve this problem, we can create a copy of the linked list before performing any operations that might modify the original list. The resulting code ensures the integrity of the original head while allowing us to check for palindrome properties effectively.

Step-by-Step Solution

Below is the modified code that respects the structure of the original list:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code

Copy Creation: The first step involves creating a separate copy of the original linked list. This allows us to manipulate the copy without affecting the original head.

Reversal of Copy: Next, we reverse this copied linked list. This is done using a simple iteration where we adjust the next pointers.

Value Comparison: Finally, we iterate through both the original linked list and the reversed copy, comparing the values at each corresponding position.

Conclusion

The solution provided not only prevents modification of the original head during the palindrome check but also maintains the structural integrity of your linked list. By following this approach, you can confidently check for palindromes without worrying about losing your original list contents.

Feel free to implement these steps in your code, and happy coding!

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