Grammarly·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Grammarly coding interview with a string manipulation problem that sounds manageable until you actually try to implement it cleanly under pressure.

Questions Asked (1)

Given a string with letters and digits, an integer k, and a window size W, repeatedly remove groups of exactly k consecutive identical characters whose starting position falls within the current sliding window (starting at index 0, advancing by one after each removal or failed attempt). Continue until no more removals are possible and return the final string.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The stack-based approach clicked for me pretty fast, keeping pairs of character and count.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem statement and edge cases, then propose a solution using a stack or linked list to efficiently track and remove groups of k identical characters. Simulate the sliding window by maintaining a pointer that advances after each removal or failed attempt, and discuss time/space complexity trade-offs.

Pro tip: Mention that using a stack of (character, count) pairs allows O(n) time by avoiding repeated scans, but be prepared to discuss how the sliding window constraint complicates this and whether a two-pointer or linked list approach might be more suitable.

1. Clarify the problem

Ask questions to confirm details: Does the window advance after a successful removal? What if multiple groups start within the window? Are removals simultaneous or sequential? Confirm input/output examples.

2. Outline a naive approach

Describe a straightforward simulation: scan the string for groups of k identical characters starting within the window, remove them, update the window position, and repeat until no removals. Mention its O(n^2) time complexity.

3. Optimize with data structures

Propose using a stack of (char, count) to track consecutive characters and enable O(1) removals when count reaches k. Explain how to incorporate the sliding window constraint, perhaps by maintaining a separate pointer or using a doubly linked list.

4. Analyze trade-offs

Compare the naive and optimized approaches in terms of time/space complexity, code complexity, and suitability for the sliding window constraint. Discuss whether the window constraint can be handled without significant overhead.

5. Test with examples

Walk through a small example to validate the approach, covering edge cases like k=1, W larger than string length, and overlapping groups.

Key Points to Mention

Time and space complexity of the proposed solution
Handling the sliding window constraint and its impact on algorithm choice
Edge cases: k=1, k > string length, W=0, no removals possible
Use of stack or linked list to efficiently track and remove groups
Potential for simultaneous vs sequential removals and how it affects the algorithm
Trade-offs between simplicity and performance in a real-world coding interview

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.