Many assume that the first round of Microsoft's technical interview is easy — a warm-up to get comfortable. But in reality, “easy” is often a trap in disguise. Today, the CSOAHELP team shares a real-life case from one of our clients — a seemingly basic parentheses validation question that nearly cost him the interview. In the end, he passed successfully with the support of our real-time remote interview assistance.
Here's the original question:
Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order.
Valid examples: (), ()[]{}, {[]}
Invalid examples: (], ([)], {[()]}
At first glance, you might say, “Isn’t this just a beginner-level LeetCode question? Use a stack and done.” It’s true this question often appears in basic problem sets. What you don’t realize is that at Microsoft, the evaluation goes far beyond writing runnable code.
Our client, a fresh graduate from a top Chinese university, was applying for a Software Development Engineer (SDE) role at Microsoft. The technical interview was conducted in English via Zoom.
After a short introduction, the interviewer shared their screen and said, “Let’s start with something simple.” The candidate immediately recognized the question and started confidently. But as he began to code, he started stumbling, losing fluency, and his thoughts became disorganized. The interviewer interrupted: “Can you explain your logic again, step by step?”
This is when he activated CSOAHELP’s real-time remote support system. His second screen was already connected to our backend, and our support engineer started monitoring the session in silence.
We quickly sent a structured textual hint: “Use a stack. Push left brackets onto the stack. When encountering a right bracket, check if the top of the stack matches. If so, pop it. Otherwise, it’s invalid. Watch out for edge cases like an empty stack or leftover elements.”
The candidate regrouped and began responding with our wording: “I’ll use a stack to track left brackets. When I encounter a right bracket, I’ll check if the stack is not empty and if the top matches. If so, I pop it. Otherwise, it’s an invalid input.”
The interviewer nodded and asked him to proceed with the code. The candidate wasn’t fast at typing, so we synced a reference implementation to his second screen to guide him:
He read while typing and explained each part as he went along. The interviewer listened carefully. Although the candidate wasn’t fluent in implementation, with our pre-prepared structure and logic, he successfully completed the function.
The interviewer then asked, “Can you tell me what edge cases might break this solution?”
We quickly provided the candidate with a list: “Empty string, single opening bracket, unmatched closing bracket, incorrect nesting order, or invalid characters.” He responded: “For example, an empty string should be valid. A single '(' should return false. Something like '([)]' should also be invalid due to incorrect nesting.”
The interviewer approved the response and asked him to run some test cases. Fortunately, the candidate had reviewed our sample cases beforehand, and he entered them confidently while explaining the expected outputs.
But the interviewer wasn’t done. He continued, “What’s the time complexity of your solution? Can it be optimized?” We immediately sent supporting notes: “Single traversal of the string, each bracket pushed and popped at most once — overall O(n) time complexity. Space complexity is also O(n) due to the stack.” The candidate paraphrased this, and the interviewer nodded.
Next came a follow-up: “If we wanted to extend this function to handle other characters beyond brackets, how would you do that?” We swiftly displayed a new suggestion: “Introduce a set of valid characters. Skip unrelated ones, or add mapping rules for new symbols.” The candidate thought out loud: “We can define a set of allowed symbols. If the current character isn’t in the set, we can skip or ignore it.”
This series of probing questions could’ve easily derailed an average candidate. But with CSOAHELP’s structured, real-time support, he handled each one with clarity and consistency. Even with limited ability, he came across as organized and composed — making a solid impression on the interviewer.
What this interview illustrates is that the difficulty lies not in the problem, but in maintaining rhythm, systematizing answers, and managing pressure. Many candidates know the answer during practice but fall apart under questioning. Our remote support doesn’t answer for you — it’s like having an invisible coach guiding your performance.
We help assess the question type, structure your response, offer keywords when you’re stuck, realign you when you drift, and even present code templates when you're implementing. With just repetition or slight adaptation, a candidate can turn a shaky session into a strong performance.
At the end of the interview, the interviewer said, “Your solution is clean and well-thought-out.” That might just be the signal of Microsoft's approval.
Not everyone can operate at 100% under pressure, but everyone deserves a shot at presenting their best self without getting derailed by nerves.
CSOAHELP’s remote interview assistance doesn't just help with technical problems — it's the difference-maker in your psychological game.
Are you ready? Because we’re ready for you.
经过csoahelp的面试辅助，候选人获取了良好的面试表现。如果您需要面试辅助或面试代面服务，帮助您进入梦想中的大厂，请随时联系我。
If you need more interview support or interview proxy practice, feel free to contact us. We offer comprehensive interview support services to help you successfully land a job at your dream company.
