Easy

Meta-styleMicrosoft-style

Reverse a Segment of a Linked List DSA Interview

Given the head of a singly linked list and two positions m and n, reverse the nodes from position m to position n in place and return the new head.

Mock Interview with AI

1. Problem Statement

You are given the head of a singly linked list and two 1-indexed positions m and n. Reverse the nodes from position m to n in place and return the new head.

2. Live Coding Format

Choose Python, JavaScript, Java, or C++, then solve while explaining your reasoning to the live interviewer.

Validation uses handwritten tests only. The MVP does not compile or run code, and it does not provide AI algorithm completion.

3. Key Focus Areas

1
Problem clarification and contract
2
Approach exploration and optimality
3
Think-aloud communication and pacing
4
Implementation correctness
5
Code quality and language fluency
6
Handwritten tests and dry run
7
Debugging and self-correction
8
Complexity analysis
9
Follow-up performance

4. What Strong Candidates Should Demonstrate

✓Clarify indexing convention and boundary behavior before coding.
✓Explain an extract-and-rebuild baseline and improve to an in-place pointer reversal.
✓Think aloud while implementing careful pointer manipulation.
✓Validate with explicit expected outputs and a top-to-bottom handwritten dry run.
✓Analyze time and space complexity and pace the easy core problem to leave room for a coding follow-up.

Evaluation Guide

This is an evaluation framework, not a single model answer. Strong designs may make different choices when their assumptions and trade-offs are explicit.

Problem clarification and contract

10%

Senior signals

✓Clarifies whether positions are 1-indexed or 0-indexed, confirms 1 <= m <= n <= length, and asks how m == n should behave.
✓Confirms whether the list is guaranteed non-empty and whether node values can repeat.

Staff-level signals

◆Raises whether this must avoid extra allocation for very long lists in a memory-constrained context.

Common red flags

×Codes immediately while assuming 0-indexing without confirming.

Approach exploration and optimality

20%

Senior signals

✓Explains an extract-values-reverse-and-rewrite baseline, identifies its extra-space bottleneck, and improves to an in-place pointer reversal using a dummy node and three pointers.
✓Explains how to reconnect the reversed segment to the unchanged parts before and after it.

Staff-level signals

◆Discusses recursive versus iterative reversal and the stack-depth tradeoff for very long segments.

Common red flags

×Starts implementation without explaining an approach even after one interviewer prompt.

Think-aloud communication and pacing

10%

Senior signals

✓Explains the plan before coding and narrates each pointer reassignment while implementing.
✓Completes the easy core problem efficiently enough to leave meaningful time for a follow-up.

Common red flags

×Writes substantial code silently and cannot explain what the code is doing.
×Spends most of the interview on the easy core problem and leaves insufficient time for a follow-up.

Implementation correctness

25%

Senior signals

✓Implements a correct in-place reversal using a dummy node (or explicit head-change handling) that reconnects the segment before m and after n without losing nodes.
✓Handles m == n, m == 1 (head changes), n == length, and a single-node list.
✓Provides a convincing step-by-step argument for the pointer reconnection.

Common red flags

×Loses a node reference mid-reversal, creating a cycle or dropping the remainder of the list.
×Final code contains a material correctness bug that the candidate does not identify.

Code quality and language fluency

15%

Senior signals

✓Produces readable, language-appropriate code with clear pointer variable names and a defined dummy-node or head-tracking pattern.

Common red flags

×Contains null-pointer risks or syntax-level incoherence that prevents credible reasoning.

Handwritten validation, dry run, and debugging

10%

Senior signals

✓Provides explicit inputs and expected outputs before tracing the code from top to bottom, drawing the list as boxes and arrows if helpful.
✓Covers m == n, head-changing reversal, tail-reaching reversal, and a single-node list.
✓Finds and fixes an error independently, then re-validates the affected path.

Common red flags

×Claims the code works without a representative trace.

Complexity analysis and follow-up

10%

Senior signals

✓States linear time and constant auxiliary space and compares them with the extract-and-rebuild baseline.

Staff-level signals

◆Discusses recursion stack space as a hidden cost if a recursive approach is chosen.

Common red flags

×Cannot state the complexity of the implemented solution.
×Fails a reasonable follow-up after solving an easy first problem, despite having at least five minutes and receiving bounded clarification.

Trade-offs to articulate

Extracting values into an array and rewriting the list is simple but uses linear extra space.
In-place iterative pointer reversal achieves constant auxiliary space but requires careful pointer bookkeeping.
Recursive reversal can be elegant but adds call-stack space proportional to segment length.

Practice follow-up questions

1.Coding follow-up: generalize the solution to reverse every consecutive group of k nodes in the entire list, leaving any final incomplete group in its original order.
2.Verbal extension: how would the approach change if the list were doubly linked instead of singly linked?

Want interactive feedback?

Practice this problem in the live coding workspace while the interviewer probes your clarification, algorithm, implementation, complexity, and handwritten tests.

Start Interview

Core Concepts

Linked ListsPointer ManipulationComplexity Analysis