Recently, one of Programhelp's North American students successfully completed the NVIDIA OA, and we reviewed the test together.
He is a CS Master at a school in California, and he has about 300 problems in Leetcode. His algorithmic foundation is not bad, but he has never done monotonic stack type problems before.
The good thing is that before the exam we arranged a few rounds of simulations to accompany the practice, focusing on the "contribution counting" and "subarray class" questions, the result of the official exam to get a solid two questions full AC.
The combination of questions this time was pretty typical, one monotonic stack question that favored algorithmic logic and one easy construction question.
The overall difficulty is moderate, but the detailing determines the scoring rate.
Q1: Sum of Subarray Minimums
Problem.
Given an integer array arr, return the sum of the minimum value of every possible subarray of arr. Since the answer may be large, return it modulo 109+710^9 + 7109+7.
Example.
Input: arr = [3, 1, 2, 4]
Output: 17
Explanation.
Subarrays are [3], [3,1], [3,1,2], [3,1,2,4], [1], [1,2], [1,2,4], [2], [2,4], [4].
Their minimums are [3,1,1,1,1,1,1,2,2,4].
Sum = 17
Thought Analysis:
This problem would have a high time complexity of O(n²) if you violently enumerate all subarrays.
A more subtle way is to "change the perspective": how many times can each element be the minimum?
Just know this "number of occurrences" and multiply it by the current value to get its total contribution.
The steps of the algorithm are as follows:
- Use a monotonically increasing stack to find the first position to the left of each element that is smaller than it is.
left[i].; - Similarly, find the first position on the right that is smaller than it
right[i].; - Contribution of the current element =
(i - left[i]) * (right[i] - i) * arr[i].; - All the contributions are summed and modeled for 109+710^9 + 7109+7.
Core Exams: Monotonic Stack + Contribution Count
Time Complexity: O(n)
This question is almost an "old friend" of NVIDIA, Amazon, and Google OA, so it's worthwhile to get good at it.
Q2: Unique Integers That Sum Up to Zero
Problem.
Given an integer n, return an array containing n unique integers that sum up to 0.
Example.
Input: n = 5
Output: [-2, -1, 0, 1, 2]
Thought Analysis:
This is a typical construction question with a low level of difficulty.
The logic is straightforward:
- If n is an even number, you can pair up two by two
[1, -1, 2, -2, ...].; - If n is odd, in addition to the pairing, add an extra
0.
Core Exams: Array construction + mathematical thinking
Time Complexity: O(n)
Participants' feelings and summaries
Participants reported that this NVIDIA OA is not a large set of questions (usually 2 questions of 70 minutes), but the logical intensity is moderate, and the "proficiency" of the algorithms is very much in question.
The first question made him say, "I'm glad I practiced the monotone stacks," and the second question ended easily.
Overall Experience:
"Time was tight, but the question sets were practiced to the point where Programhelp's voice reminders of the pace were so helpful, and the pace of the questions was much more steady."
Extended Recommendations
If you are preparing for a software engineering position at NVIDIA, AMD, Intel, or Qualcomm, you can focus on reviewing:
- Monotonic stacks, prefixes and suffixes contribute to the counting class of questions
- Constructed questions (balance / symmetric sum)
- Modal arithmetic and boundary control
In addition, it is recommended to practice more timed simulation questions to simulate the real OA time pressure.
FAQ Frequently Asked Questions
Q1: Is NVIDIA's OA difficult?
A: Overall moderate to high, with a bias towards algorithmic logic and few pure implementation questions. Usually contains 2-3 questions and should be completed within 70 minutes.
Q2: Are there any language restrictions?
A: The platform supports multiple languages (Python, C++, Java). Python users need to pay special attention to the timeout problem, and it is recommended to familiarize with the input/output mode in advance.
Q3: What types of algorithms are tested more?
A: NVIDIA OA favors "contribution class" questions (monotonic stacks, prefix/postfix products, sliding windows), construction questions, and array/string processing. DP and graph questions are less common.
Q4: What should I do if I get stuck on a question?
A: If it is a formal test environment, you can use Programhelp's remote voice helper service in advance, and we will prompt the ideas and code boundaries in real time to help stabilize the output results within the time limit.
OA No Trace Assists｜Programhelp Practical assistance program
Companies like NVIDIA start to "sift the mind" at the OA stage, not just to be able to write code, but also to be responsive and clearly structured.
Many students obviously can usually write, once the formal written test is stuck in the details, or not enough time.
This is where Programhelp comes into play.
At our core -- remote real-time voice alerts + no-touch online coaching.
You're answering normally in the question and answer screen, and we're watching the progress in real time, in the background.
Voice prompts at key nodes "Consider boundaries here", "Complexity can be optimized a bit more", and
There are no screen traces or input interference throughout, and the platform does not detect any external connections.
We've helped over 300+ North American CS students pass OA at top companies like NVIDIA, Amazon, Stripe, Citadel, IMC, and many more.
The overall pass rate is as high as 96%+.
