Count median in linked list
Last updated: September 7, 2025
Quick Overview
Given a singly linked list of integers, write a function to find and return the median value of the elements in the list. The median is defined as the middle value when the numbers are sorted; if there is an even number of elements, return the average of the two middle values. Your function should handle edge cases, such as an empty list, appropriately.
DoorDash
September 7, 20254
12
513 solved
Given a singly linked list of integers, write a function to find and return the median value of the elements in the list. The median is defined as the middle value when the numbers are sorted; if there is an even number of elements, return the average of the two middle values. Your function should handle edge cases, such as an empty list, appropriately.
This coding problem is frequently asked during Onsite at DoorDash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. DoorDash expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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 you parallelize this solution?
- How would your solution change if the input was sorted?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To find the median in a singly linked list, we need to determine the middle value(s) of the list when sorted. Since the linked list does not allow random access, we cannot directly sort it like an arr...
Approach
- Count the Elements: Traverse the linked list to count the total number of elements (
n). - Determine Median Position: If
nis odd, the median is the(n // 2)-th element. Ifnis eve...
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