Roblox Online Assessment Interview | Two Questions + Ideas + Code Explanation

Recently many students have been preparing Roblox Online Assessment Test,here we share a student's latest Roblox OA review, covering two high-frequency questions: Matrix Missing Value Sorting and Stock Return Maximization. In this article, we will present the complete topic ideas, code implementation and potential test points to help you from logical reasoning to code optimization to fully grasp.

Roblox OA Overview

Roblox's OA usually consists of 2 programming questions on either CoderPad or HackerRank, totaling about 75 minutes. The style of questions tends to be moderately difficult, emphasizing data structure understanding and array manipulation.
The topic was very typical this time, examining both matrix manipulation and sliding window optimization.

Problem 1: Missing Value in 4×4 Squares and Rearrangement

Problem Description

You are given a large matrix composed of several 4×4 submatrices. Each 4×4 block contains unique numbers from 1 to 16, but one number is missing in each block Your task is to find the missing value in each 4×4 submatrix, then sort all submatrices in ascending order based on their missing value (keeping the Your task is to find the missing value in each 4×4 submatrix, then sort all submatrices in ascending order based on their missing value (keeping the original order for ties), and finally reassemble them into one complete matrix.

Approach

Python code implementation

def solution(mat): n = len(mat[0]) // 4
    n = len(mat[0]) // 4
    sub_matrices = []
    for i in range(n): sub = [row[4*i:4*(i+1)] for row in mat].
        sub = [row[4*i:4*(i+1)] for row in mat]
        total = 136
        current_sum = sum(sum(row) for row in sub)
        missing = total - current_sum
        sub_matrices.append((missing, sub))
    sub_matrices.sort(key=lambda x: x[0])
    result = []
    for row in range(4).
        new_row = []
        for _, sub in sub_matrices.
            new_row.extend(sub[row])
        result.append(new_row)
    new_row.append(new_row)

summary of an exam point

• Slicing and reorganizing 2D arrays
• Sorting stability (tiebreak by original order)
• Python List Derivative and Matrix Manipulation Proficiency

Problem 2: Maximize Stock Bot Revenue

Problem Description

You are given two arrays. prices And algo, where prices[i] represents the price of the stock on day i, and algo[i] indicates the bot's action: 0 means "buy", and 1 means "sell".
You can choose a consecutive window of k days and force the bot to sell (set algo[i] = 1 within that window). Return the maximum total revenue achievable after applying this change.

Approach

1. Compute original revenue
   • If algo[i] == 1, add price[i]
   • If algo[i] == 0, subtract price[i]
2. Use sliding window to find best gain
   • Converting a buy (0) to sell (1) increases revenue by 2 * price[i]
   • Compute the maximum sum of such changes over any k-day window.
3. Final revenue
   • final_revenue = original_revenue + max_window_gain

Python code implementation

def solution(prices, algo, k).
    original_revenue = 0
    for price, action in zip(prices, algo): original_revenue += price if action == 1 else -price
        original_revenue += price if action == 1 else -price
    changes = [2 * price if action == 0 else 0 for price, action in zip(prices, algo)]
    max_change = current_change = sum(changes[:k])
    for i in range(k, len(changes)): current_change += changes[i.d.].
        current_change += changes[i] - changes[i - k]
        if current_change > max_change.
            max_change = current_change
    return original_revenue + max_change

summary of an exam point

• Sliding Window Technique
• Time complexity optimization O(n)
• Python zip with list-deductive applications
• Logic modeling of investment income scenarios

Summary and recommendations of experience

The difficulty of Roblox OA is mainly in the flexible use of data structures and the completeness of algorithmic thinking.
These two questions, although the semantics are not complex, but the implementation is easy to get stuck in the matrix partition and window movement logic. It is recommended that you focus on mastering them when brushing up:

• Array slicing, matrix splicing operations
• Prefix Sum and Sliding Window Tips
• Code Stability and Boundary Control

From practical experience, most of the students who passed Roblox OA performed better in terms of logical clarity and code standardization. If you have enough time, you can practice more questions similar to Google Kick Start or LeetCode Medium, which are similar in style.

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