Moloco Interview Questions — Page 2

Moloco·Machine Learning Engineer·Technical Phone Screen

Jun 2026

Interviewed for an ML Engineer role at Molocoads and got hit with a pure algorithms problem. Stack-based string manipulation, nothing ML about it, but I guess they want to know you can actually code.

Given a string and an integer k, repeatedly remove groups of k adjacent identical characters until no such group exists. Return the resulting string. What's an O(n) solution?

“The naive approach is obvious and they probably expect you to dismiss it quickly.”

View Post

Moloco·Software Engineer·Onsite - System Design / Architecture

Jun 2026

Round 2 at Molocoads for a software engineering role, system design with a Korean interviewer who was pretty chill. Just the one question but it had some depth to it.

Design a real-time comment system similar to Facebook's.

“This is one of those questions where you think you know where to start and then realize halfway through that the 'real-time' part is doing a lot of heavy lifting.”

View Post

Moloco·Machine Learning Engineer·Online Assessment (OA)

Jun 2026

Two-question OA for a Machine Learning Engineer role at Molocoads. Both problems were algorithmic, nothing ML-specific, which was a bit of a surprise. The grid simulation one was the trickier of the two.

Given an m x n grid of integers, repeatedly eliminate any cells that are part of a horizontal or vertical run of 3 or more equal values (all in the same round, simultaneously), set them to zero, then apply gravity so non-zero values sink to the bottom of each column. Keep going until no more eliminations are possible. Return the final grid.
Given two large lists of strings A and B, find the maximum possible length of a longest common prefix between any pair (a, b) where a is from A and b is from B. The input is too large for a brute-force pairwise comparison.

“The simultaneous marking tripped me up at first.”

View Post

Moloco·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at Molocoads for a software engineer role, centered entirely on building a search autocomplete system at Google scale. Pretty deep dive, lots of follow-ups on the data pipeline and serving layer.

Design a search autocomplete (typeahead) system that can handle billions of queries per day, returning the top-K completions for a given prefix ranked by popularity, with sub-100ms latency at p99.
How would you handle real-time trending queries in the autocomplete system without blowing up your serving infrastructure?
Walk me through how you'd shard and replicate the serving layer, and what happens when a shard goes down.
How would you incorporate personalization, locale handling, and safety filtering (e.g. suppressing illegal or harmful completions) into the system?

“This is one of those questions where you think you know it cold and then the follow-ups expose every gap.”

View Post

Moloco·Software Engineer·Technical Phone Screen

Jun 2026

Interviewed for a software engineer role at Molocoads and got a range-sum problem that started simple and then got progressively harder. The follow-up about making it mutable is where things got interesting and I felt a bit underprepared for the full tradeoffs discussion.

Design a data structure that supports efficient range sum queries on an integer array, first for an immutable array, then extended to support point updates as well. Both operations should scale to arrays and query counts in the hundreds of thousands.

“Part one was fine, prefix sums, done in two minutes.”

View Post

Moloco·Software Engineer·Technical Phone Screen

Jun 2026

Did a coding round for a Software Engineer role at Molocoads with two algorithm problems. Nothing too wild, but the second one had me second-guessing my approach the whole time.

Given a list of rooms where each room contains keys to other rooms, determine whether you can visit all rooms starting from room 0.
Given a balanced parentheses string, compute its score using the rules: "()" = 1, concatenation adds scores, and wrapping a string in parens doubles its score.

“Graph traversal problem basically.”

View Post

Moloco·Data Scientist·Recruiter / HR Screen

Jul 2026

HR screen for a data science intern role at Moloco. Pretty standard opener, just the usual 'why us' question to kick things off.

Why do you want to work at Moloco, and what are you hoping to get out of your next role?

“I fumbled this a bit because I hadn't tied my answer closely enough to what Moloco actually does.”

View Post

Moloco·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Molocoads for a software engineer role, centered entirely on building an autocomplete service at scale. Pretty deep dive, they wanted opinions on everything from cache layers to update pipelines, not just a high-level sketch.

Design a large-scale autocomplete service that returns the top 5 query suggestions within 100ms as a user types, ranked by popularity and recent trends.
How would you design the API for an autocomplete service, and what does the data model look like underneath it?
How would you handle sharding and hot prefixes in a high-traffic autocomplete system?
Walk through your cache design for this system, including what you cache, at what layer, and how you handle invalidation.
Describe the offline and online pipelines you'd build to keep autocomplete suggestions fresh and updated from new search logs.

“This is a meaty one and I underestimated how many sub-problems were hiding inside it.”

View Post