How MongoDB Interviews in 2026: Process, Questions & What They Score

1. 01

   Group Anagrams: group a list of words so that anagrams end up in the same group.

   Tests hash-map grouping by a canonical key such as sorted characters or character counts.

2. 02

   Valid Parentheses: determine whether a string of brackets is balanced.

   Tests stack-based matching of nested bracket pairs.

3. 03

   Word Break: decide whether a string can be segmented into a sequence of dictionary words.

   Tests dynamic programming over string prefixes against a dictionary set.

4. 04

   Text Justification: format a list of words into lines of a fixed width with even spacing.

   Tests careful greedy line-fitting and even space distribution across words.

5. 05

   Versioned Datastore: implement PUT and GET so that a read returns the value as of a given timestamp.

   Tests API design plus a sorted-by-timestamp lookup such as binary search.

6. 06

   Union Iterator: build an iterator that merges several already-sorted inputs into one sorted stream.

   Tests k-way merge logic, directly analogous to merging sorted index scans.

7. 07

   Dynamic Product Queue: design a structure supporting insertion, querying the product of the current elements, and FIFO eviction, handling zeros correctly.

   Tests handling the zero-value edge case in a running-product data structure.

8. 08

   Design a function that performs a regex-like operation on a string.

   Tests pattern-matching logic, typically via recursion or dynamic programming.

9. 09

   Convert a given array into a linked list.

   Tests keeping insertion O(1) by tracking a tail pointer.

10. 10

    Implement a queue using arrays.

    Tests circular-buffer boundary conditions and modulus-based index wraparound.

11. 11

    Find the length of the path from node A to node B in a binary tree.

    Tests locating the lowest common ancestor and summing depths from it.

12. 12

    Given a matrix containing only 1s and 0s, find the largest square sub-matrix which contains only 1s.

    Tests a 2D dynamic programming recurrence over matrix cells.

13. 13

    Egg dropping problem: given 2 eggs and a 100-floor building, find the minimum number of drops required.

    Tests the classic dynamic programming optimization for worst-case drop count.

Reported problems, listed so you know what to expect. Practice them in your own editor or on the platform you prefer; SupaCV's practice mode coaches how you talk through them.

1. 01

   Implement a concurrent blocking queue.

   Tests thread-safe producer-consumer coordination with blocking semantics.

2. 02

   Implement a high-concurrency LRU cache.

   Tests combining LRU eviction with fine-grained locking under contention.

3. 03

   Build an in-memory key-value store.

   Tests persistence, eviction and thread-safety trade-offs in a simple store.

4. 04

   Implement a thread-safe rate limiter.

   Tests a concurrency-safe token-bucket or sliding-window algorithm.

5. 05

   Implement an inverted index.

   Tests mapping terms to document lists, mirroring text-search indexing.

6. 06

   Implement a basic query parser.

   Tests tokenizing and parsing a small query grammar into an executable form.

Reported problems, listed so you know what to expect. Practice them in your own editor or on the platform you prefer; SupaCV's practice mode coaches how you talk through them.

1. 01

   How would you replicate data across multiple data centers?

   Tests trade-offs between NoSQL replication options and custom sync design.

2. 02

   Whiteboard the design of a system you are currently working on.

   Tests defending real architecture trade-offs from your own project under questioning.

3. 03

   Design a SIM card store system that hands out 3 SIM cards on demand, with unpredictable 10-digit numbers, efficient storage and fast retrieval.

   Tests trie-based storage for fast prefix retrieval of random numbers.

4. 04

   Explain the CAP theorem in layman's terms and where it applies in distributed systems.

   Tests plain-language grasp of consistency, availability and partition tolerance trade-offs.

5. 05

   Design a distributed logging system.

   Tests throughput, ordering and durability trade-offs in a log pipeline.

6. 06

   Design a database migration platform.

   Tests schema mapping and cutover strategy design, mirroring Relational Migrator.

7. 07

   Design a disaster recovery system.

   Tests RPO and RTO trade-offs and a correctness argument for failover.

8. 08

   Design a sharding balancer: how do you decide when and what to move between shards?

   Tests chunk-splitting and balancing logic to avoid hot shards.

9. 09

   Walk through a replica set election: how is a new primary chosen and what can go wrong?

   Tests consensus, majority write concern and split-brain avoidance reasoning.

Reported problems, listed so you know what to expect. Practice them in your own editor or on the platform you prefer; SupaCV's practice mode coaches how you talk through them.

1. 01

   Nth Highest Salary: return the nth highest value from a dataset, in SQL and in the MongoDB equivalent.

   Tests translating SQL ranking logic into aggregation-pipeline stages.

2. 02

   How would you optimize an aggregation pipeline?

   Tests stage ordering, early filtering and index-eligible pipeline stages.

3. 03

   How do you read a query plan from explain() and use it to fix a slow query?

   Tests distinguishing a collection scan from an index scan and fixing it.

4. 04

   How do you approach schema design in a document database?

   Tests embedding-versus-referencing trade-offs for a given access pattern.

5. 05

   Compare NoSQL and SQL databases, and explain ACID properties.

   Tests knowing when relational guarantees matter versus document flexibility.

6. 06

   Which design patterns have you used, and when would you reach for singleton, builder or factory?

   Tests recognizing which creational pattern fits a given object-construction problem.

7. 07

   What is MongoDB?

   Tests basic product literacy about the document database you would be building.

Reported problems, listed so you know what to expect. Practice them in your own editor or on the platform you prefer; SupaCV's practice mode coaches how you talk through them.

1. 01

   Tell me about a time when you had to mediate a conflict.

2. 02

   Tell me about a time when you received negative feedback and how you handled it.

3. 03

   Describe a situation where you were given an ambiguous task or vague instructions. How did you clarify expectations?

4. 04

   Tell me about a technical challenge that you have overcome.

5. 05

   What was the hardest challenge you have faced in your career?

6. 06

   What was the most difficult bug you solved?

7. 07

   What is your favourite programming language and why?

8. 08

   Describe a project where you took initiative or demonstrated leadership.

9. 09

   Tell me about a time you failed and what you learned from it.

10. 10

    Why are you interested in MongoDB, and why this team?

11. 11

    What are you looking for in your next role, and what are your goals and aspirations for the future?