Karat·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026Remote

Summary

Karat screen for a Software Engineer role, just one coding problem the whole time. The question was a password validator where you return every rule that gets broken. Seemed manageable at first but there were enough edge cases to keep you honest.

Questions Asked (1)

Given a password string and a set of three special characters, validate the password against five rules and return a list of all the rules it violates. Rules cover minimum length (over 15 chars), absence of the substring 'password' (case-insensitive), presence of both upper and lowercase letters, at least one of the given special characters, and no character repeating more than four times consecutively.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The consecutive repeat rule is where I fumbled a bit.

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AI HintsAI Generated

Suggested Approach

Clarify the exact rules and edge cases, then design a single-pass solution that checks all conditions while tracking consecutive repeats. Use efficient string operations and return a list of violated rule identifiers.

Pro tip: Discuss trade-offs between a single-pass approach and separate checks; mention that a single pass is more efficient but may be less readable, and propose a clean implementation with helper functions.

1. Clarify requirements and edge cases

Confirm the exact rules, the format of the returned list, and how to handle edge cases like empty strings or null inputs.

2. Design the algorithm

Plan a single-pass approach that checks all rules simultaneously, tracking consecutive character repeats and using efficient string operations.

3. Implement the solution

Write clean code with helper functions for each rule, or a single loop that updates violation flags, ensuring case-insensitive checks where needed.

4. Test and validate

Test with various inputs covering all rules, including edge cases like exactly 15 characters, repeated characters, and mixed cases.

5. Discuss trade-offs and optimizations

Explain time and space complexity, and consider alternative approaches like regex for certain checks, weighing readability vs performance.

Key Points to Mention

Time and space complexity analysis (O(n) time, O(1) space for single pass).
Handling case-insensitive checks for 'password' substring and character types.
Tracking consecutive repeats efficiently without extra space.
Using sets for special characters and character type checks.
Returning a list of violated rule identifiers in a consistent order.
Edge cases: empty string, null input, exactly 15 characters, multiple violations.

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