### Approach To determine if a linked list is a palindrome, we need a structured method that efficiently checks if the sequence of values in the linked list reads the same forwards and backwards. Here’s a step-by-step breakdown of a common approach: 1. **Identify the Midpoint**: Use the slow and fast pointer technique to find the middle of the linked list. 2. **Reverse the Second Half**: Reverse the second half of the linked list starting from the midpoint. 3. **Compare the Two Halves**: Traverse both halves of the linked list simultaneously and compare the values. 4. **Restore the List (optional)**: If necessary, reverse the second half again to restore the original linked list. ### Key Points - **Clarity on Palindrome**: A palindrome reads the same from both ends. For example, the linked list 1 -> 2 -> 2 -> 1 is a palindrome. - **Efficiency**: The method should ideally run in O(n) time complexity and use O(1) additional space. - **Handling Edge Cases**: Consider cases like empty linked lists or lists with a single node. ### Standard Response To determine if a linked list is a palindrome, I employ a systematic approach that involves several key steps: 1. **Finding the Midpoint**: - I utilize two pointers, one (`slow`) moving one step at a time and the other (`fast`) moving two steps at a time. - When the `fast` pointer reaches the end of the list, the `slow` pointer will be at the midpoint. ```python def find_mid(head): slow = head fast = head while fast and fast.next: slow = slow.next fast = fast.next.next return slow # Midpoint ``` 2. **Reversing the Second Half**: - I reverse the second half of the linked list starting from the midpoint. - This can be done by iterating from the midpoint to the end and reversing the links. ```python def reverse_list(head): prev = None current = head while current: next_temp = current.next current.next = prev prev = current current = next_temp return prev # New head of the reversed list ``` 3. **Comparison**: - After reversing the second half, I compare it with the first half. - If all corresponding values match, the linked list is a palindrome. ```python def is_palindrome(head): if not head or not head.next: return True mid = find_mid(head) second_half_start = reverse_list(mid) first_half_iter = head second_half_iter = second_half_start while second_half_iter: if first_half_iter.val != second_half_iter.val: return False first_half_iter = first_half_iter.next second_half_iter = second_half_iter.next return True ``` 4. **Restoring the List**: - If the integrity of the linked list needs to be preserved, I can reverse the second half again post-comparison. ### Tips & Variations #### Common Mistakes to Avoid: - **Not Handling Edge Cases**: Failing to check for empty or single-node lists can lead to incorrect assumptions. - **Overcomplicating the Logic**: Keeping the algorithm straightforward enhances both readability and maintainability. #### Alternative Ways to Answer: - For roles requiring optimization, mention alternative methods like using a stack to store values from the first half and then comparing with the second half. - Discuss the complexity of the solution, emphasizing the trade-offs between time and space. #### Role-Specific Variations: - **Technical Roles**: Focus on the implementation details, time complexity analysis, and edge cases. - **Managerial Roles**: Emphasize how this method can be adapted in team settings to solve similar algorithmic challenges. - **Creative Roles**: Highlight the importance of problem-solving and algorithmic thinking in design and development processes. ### Follow-Up Questions - **What other data structures could you use to solve this problem?** - **How would your approach change if the linked list contains a large number of elements?** - **Can you explain the time and space complexity of your solution?** - **What would you do if the linked list was a doubly linked list instead?** By following this structured approach, job seekers can effectively demonstrate their problem-solving skills and technical knowledge during interviews, particularly for positions requiring algorithmic proficiency