Roblox OA Experience: Mini-Games + Coding, Two Coding Problems Fully Solved

The Roblox OA is quite different from a typical Big Tech coding assessment. Instead of focusing entirely on LeetCode-style problems, the assessment combines several timed mini-games and decision-making tasks before moving into the actual Coding Skills section.

The overall format felt somewhat similar to the modular, time-limited structure used by companies like Optiver. Each section has its own fixed time limit, and once you start a section, you cannot switch to another one. Managing your time and staying focused is therefore really important.

Roblox OA Format

My assessment was roughly divided into the following sections:

• Robots: 25 minutes
• Factories: 25 minutes
• Decision-Making: 25 minutes
• Outpost: Mars: 40 minutes
• Coding Skills: 50 minutes / 2 problems

The first four sections are not traditional programming questions. They are more focused on following instructions, making decisions quickly, and adapting to the rules of each mini-game.

Once you enter a section, the timer is locked to that section, so you cannot pause it and come back later. Keeping track of your time is especially important.

Coding Skills: Two Problems

I got full credit on both coding problems. The two questions were quite different in style, but neither required an extremely complicated algorithm.

Problem 1: Reordering 4×4 Matrices with Missing Numbers

You are given a large matrix with dimensions 4 × (4 × n). It consists of n separate 4×4 matrices placed side by side.

Each 4×4 matrix has one missing number represented by ?.

The task is to:

1. Find the missing number in each 4×4 matrix.
2. Fill in the missing value.
3. Sort the 4×4 matrices by their missing values in ascending order.
4. If two matrices have the same missing value, preserve their original relative order.
5. Combine the sorted matrices back into the original large matrix format.

The key observation is that the sum of all numbers in a complete 4×4 matrix is:

1 + 2 + ... + 16 = 136

So for each small matrix, the missing value can be calculated as:

missing value = 136 − sum of the existing values

After filling in the missing values, the rest is essentially matrix slicing + stable sorting.

The main implementation challenge is correctly splitting the large matrix into individual 4×4 blocks and then putting the sorted blocks back together.

Problem 2: Stock Trading Robot and Maximum Profit

The second problem was more algorithmic.

You are given:

• prices: the stock price for each day
• algo: the robot's original action for each day, where 0 means buy and 1 means sell

The robot performs exactly one action per day. You are allowed to choose one consecutive interval of length k and change all actions in that interval to sell.

The goal is to maximize the total profit.

The easiest way to think about it is to first calculate the profit using the original strategy.

Then, for every day where the original action is buy, changing that action to sell increases the profit by:

2 × price

For days that are already sell actions, changing them has no additional effect.

Therefore, we can construct a gain array representing the additional profit obtained by changing each position to sell.

Now the problem becomes finding the maximum sum of a consecutive subarray of length k.

That can be solved efficiently with a sliding window:

1. Calculate the original trading profit.
2. Build the gain array.
3. Calculate the sum of the first window of length k.
4. Slide the window across the array while maintaining its sum.
5. Take the maximum gain.
6. Return base profit + maximum gain.

The overall complexity is O(n), which is enough for large inputs.

My Takeaways from the Roblox OA

The biggest difference between this assessment and a traditional coding OA is that coding is only one part of the entire evaluation.

For the non-coding sections, I would recommend following the instructions carefully and avoiding spending too much time getting stuck on one task. Since each section has its own fixed timer, losing several minutes in one section can be costly.

For the Coding Skills section, 50 minutes for two problems is tight but manageable. In my case, the first problem was mainly about matrix manipulation and stable sorting, while the second was based on calculating the original result and then using a sliding window to optimize the modified strategy.

If you're preparing for Roblox, it is worth practicing problems involving matrix slicing, stable sorting, simulation, sliding windows, and strategy optimization. These patterns can be more useful here than simply memorizing a large number of advanced algorithms.

Final Thoughts

Overall, I found the Roblox OA quite interesting because it tests more than just coding speed. The combination of mini-games, decision-making, and programming makes the assessment feel noticeably different from a standard Big Tech OA.

If you're preparing for Roblox or other Big Tech OA/VO interviews, you can also check out Interview Show for more interview experiences, OA questions, and preparation resources.