Count median in linked list
Last updated: April 4, 2026
Quick Overview
Given a singly linked list of integers, write a function to calculate and return the median value of the elements in the list. If the list has an odd number of elements, return the middle element; if it has an even number of elements, return the average of the two middle elements. The function should handle edge cases, such as an empty list, by returning a suitable value (e.g., None).
xAI
April 4, 202642
6
301 solved
Given a singly linked list of integers, write a function to calculate and return the median value of the elements in the list. If the list has an odd number of elements, return the middle element; if it has an even number of elements, return the average of the two middle elements. The function should handle edge cases, such as an empty list, by returning a suitable value (e.g., None).
This coding problem is frequently asked during Technical Screen at xAI. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. xAI expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would your solution change if the input was sorted?
- How would you modify your solution to handle streaming input?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
To find the median of a linked list, we need to analyze the structure and properties of linked lists. Since linked lists do not allow random access like arrays, we cannot directly access the middle el...
Approach
We will implement the following step-by-step algorithm:
- Check for Edge Cases: If the linked list is empty (head is None), return None.
- Count Elements: Initialize a count variable and a c...
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