I recently completed Tesla's Online Assessment on the HackerRank platform. The assessment consisted of three Tesla OA Questions, and I ended up writing around 200 lines of code in total. Overall, the difficulty was moderate. I finished all three problems in roughly 30 minutes and passed every test case successfully. Since I've completed quite a few online assessments from major tech companies this year, the overall workflow felt familiar, leaving enough time to review edge cases before submitting.
Tesla OA Questions Breakdown
Question 1: SQL Score Statistics
The first problem involved two database tables:
- test_groups — stores group names and the score assigned to each test case.
- test_cases — stores test case IDs, their corresponding group, and execution status.
The task required using test_groups as the primary table and performing a LEFT JOIN with test_cases. For every group, we needed to calculate:
- Total number of test cases
- Number of passed test cases
- Total score earned
Finally, the output had to be sorted by total score in descending order and group name in ascending order.
The implementation was fairly straightforward. I used a LEFT JOIN to ensure every group appeared even if no test cases existed. The total number of test cases came from counting the primary key, while passed cases were counted using a CASE WHEN expression checking for the status 'OK'. The final score was simply the number of passed test cases multiplied by the score value stored in test_groups.
Question 2: Text Transcription (Maximum Insertions of 'a')
Given a lowercase string S, the goal was to insert as many lowercase 'a' characters as possible while ensuring that the resulting string never contained three consecutive 'a' characters.
If the original string already contained "aaa", the answer should immediately be -1.
Otherwise, every non-'a' character naturally separates the string into multiple independent gaps, including the beginning and the end of the string. Since each gap can contain at most two consecutive 'a' characters, the maximum number of insertions can be calculated based on the number of available gaps. After accounting for the existing 'a' characters already present, the remaining capacity gives the final answer.
The solution only requires a single linear scan, making it both simple and efficient.
Question 3: Zero Sum Fragments
Given an integer array A, count how many contiguous subarrays have a sum equal to zero. If the answer exceeds one billion, return -1.
This is a classic prefix sum and hash map problem.
I initialized a hash map with:
{0: 1}This represents that a prefix sum of zero has appeared once before processing any elements.
While traversing the array, I continuously updated the running prefix sum. Whenever the same prefix sum appeared again, every previous occurrence represented another zero-sum subarray ending at the current position. Therefore, I simply added the existing frequency stored in the hash map to the answer. Afterward, I updated the frequency of the current prefix sum. If the accumulated count exceeded one billion, the function immediately returned -1.
This algorithm runs in O(N) time and is the standard optimal solution.
Overall Difficulty
Overall, Tesla's Online Assessment was moderate in difficulty.
- The SQL question mainly tested joins, aggregation, and conditional counting.
- The string problem focused on greedy thinking and careful edge-case handling.
- The array problem tested familiarity with prefix sums and hash tables.
If you've practiced similar HackerRank problems before, the patterns become fairly recognizable, allowing you to finish comfortably within the time limit.
Preparation Tips for Tesla OA
- Become comfortable with LEFT JOIN, GROUP BY, COUNT, and CASE WHEN in SQL.
- Practice greedy string manipulation problems involving insertion and boundary conditions.
- Master the Prefix Sum + Hash Map technique for subarray sum problems.
- Spend some time getting familiar with HackerRank's coding environment and input/output format before the assessment.
Final Thoughts
Although Tesla's Online Assessment provides a reasonable amount of time, preparation still makes a significant difference. Many of these problems follow recognizable patterns, so practicing common HackerRank question types beforehand can dramatically improve both speed and confidence during the test.
If you're preparing for Tesla or other major technology companies and would like additional interview or OA support, you can learn more at Interview Aid, which provides resources and assistance for coding assessments and technical interview preparation.
Good luck with your Tesla OA, and feel free to share your own experience with other candidates preparing for upcoming assessments!
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