What is an Odd Even Linked List?

An odd even linked list involves rearranging the nodes of a singly linked list so that all odd-indexed nodes appear before even-indexed nodes. This problem tests your skills in manipulating linked lists, which is a common topic in technical interviews.

Problem Overview

Given a linked list, the challenge is to group all nodes at odd indices before the nodes at even indices. The original relative order of the nodes should be preserved. For example, if the linked list is 1 → 2 → 3 → 4 → 5, the expected output after rearranging is 1 → 3 → 5 → 2 → 4.

Steps to Solve the Problem

1. Initialize Pointers: Create two pointers, one for odd and one for even nodes. You will also need a pointer to the head of the even indexed nodes.
2. Traverse the List: Loop through the linked list, and for each node, assign it to the odd or even list based on its index.
3. Connect the Two Lists: At the end of the traversal, connect the last node of the odd list to the head of the even list.
4. Return the Rearranged List: The head of the odd list will be your new head.

Example Code Implementation

Here is a simple approach to implement the above logic in Python:

PythonCopy code

Interview Questions

1. Question: What approach do you take to implement the odd even linked list solution?

   • Answer: Start by defining a function that handles the head of the linked list. Initialize pointers for both odd and even nodes. Loop through the list while maintaining the links for both odd and even nodes, then connect the last odd node to the head of the even nodes before returning.

2. Question: Why is it important to maintain the original order of nodes while rearranging them?

   • Answer: Maintaining the original order is crucial since the problem specifies that the relative order of nodes should remain unchanged. Failure to do so would mean the solution does not satisfy the problem's requirements.

3. Question: Can you handle edge cases such as an empty list or a list with one node?

   • Answer: Yes, handle these cases at the beginning of the function. If the list is empty or has only one node, return the head immediately since there’s nothing to rearrange.

4. Question: How would you modify the code if the linked list was doubly linked?

   • Answer: In a doubly linked list, you'd need to account for both next and prev pointers. The basic logic remains the same, but when reconnecting nodes, make sure to adjust both links accordingly.

Complexity Analysis

• Time Complexity: O(n), where n is the number of nodes in the linked list. This is because we will traverse the list once.
• Space Complexity: O(1), since we are rearranging the list in place without using additional structures.

Key Takeaways

Rearranging nodes based on their indexes in a linked list demonstrates vital skills in algorithm design and data structure manipulation. Practicing this problem can enhance your understanding of linked list operations and preparation for technical interviews. Make sure to explain your thought process and approach clearly during interviews, as this can make a strong impression on your interviewers.