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Nikhil Sharan

@nikhil_twopointers

I teach DSA and system design on YouTube (Two Pointers, 1.2M). Ex-SDE at two product companies, now teaching full time. Dry run everything. No paid course here, only free stuff and honest opinions.

  • Bengaluru, India
  • Hindi · English
  • Joined May 2026
  • Last posted Oct 18, 2026
  • 2-week streak

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Everything this author has published.

Nikhil Sharan3.4K
t/interview_horror3 min

Mock interview breakdown: she solved it and still got "no hire". Here is the scorecard.

Kunal and I have been doing free mock interviews on weekends this month. One of them taught me more than the others, so with the candidate's permission (and details changed) here is the full breakdown. She solved the problem. Her code was correct. In a real loop she would have got a "lean no hire". Let us see why. The question type A merge intervals variant. Medium difficulty. Nothing exotic. Minute by minute 0-3:…

11

  • Sneha Kulkarni
    the "say done only after dry running your own example" rule. i lost a round last month by saying "done" and the interviewer immediately typed [] as the input. silence. 💀
  • Kunal Bhatia
    I was the interviewer on this one. The "defending instead of listening" at minute 18 is the one I see most. The follow-up is a gift and people treat it like an attack.
Nikhil Sharan6.8K
t/interview_horror5 min

System design primer: design a rate limiter, with real numbers

Most rate limiter answers I hear in mocks are one box on a diagram labelled "rate limiter" and then the candidate moves on. That box is the whole question. Let us do it properly, with numbers. Thanks to Kenji for reviewing the draft. 1. Requirements (spend 5 minutes here) Public API behind a gateway. 10 million daily active users. Limit: 100 requests per user per minute. Some endpoints (login, OTP) much stricter.…

17

  • Marcus Johnson
    From the on-call side: whatever you build, log every 429 with the key and the rule that fired. The first incident will be a big customer behind one NAT IP getting throttled as "one user". Ask me how I know.
  • Danny Cho
    Strongly agree on fail open vs fail closed per endpoint. One more: put a small local token bucket in each gateway process in front of Redis. If Redis gets slow, the local bucket stops abusive clients from turning a Redis brownout into an outage.
    1 reply
Nikhil Sharan63K
t/interview_horror5 min

Read the constraints first: how I pick the pattern in under 2 minutes

Most people read the story in a problem and skip the constraints. The story is decoration. The constraints tell you the complexity you are allowed, and the complexity tells you the pattern. This is the routine I use, and the one I have been teaching in mocks for six years. Step 1: constraints → your budget Rough rule: a judge does about 10^8 simple operations per second in C++ or Java. So: n ≤ 20 : exponential is…

35

  • Mahin Hasan
    constraints table is basically what every CF guy does without thinking. two corrections tho: n ≤ 500 can also take O(n² log n) comfortably, and 10^8/sec is for simple ops in C++. python is like 10^7 on a good day
    1 reply
  • Meenal Deshpande
    Coming back to DSA after a 6 year break, and this is the first cheat sheet that explains why and not only what. PFB my query (haha, old habits): is the prefix sum + hashmap approach expected from freshers or only experienced people? Thank you Nikhil sir.
    1 reply
Nikhil Sharan2.4K
t/compiling4 min

Binary search on the answer: when nothing is sorted but you can still binary search

Students learn binary search as "find x in a sorted array" and then get stuck on questions where nothing is sorted. The trick is that you are not searching the array. You are searching the answer . The problem You have packages with weights w[i] that must be shipped in order. A ship carries them over D days, loading packages in order each day until the next one would exceed its capacity. What is the minimum capacity…

9

  • Sneha Kulkarni
    ok this one is going in the notes. "feasible(x) is monotonic" is the sentence i was missing for 3 days on koko bananas
Nikhil Sharan3.7K
t/desi_devs3 min

DSA is not useless for real jobs. Grinding 800 questions without revision is.

Every few weeks the same fight starts in my comments. One side says DSA is useless because "real jobs are CRUD". The other side says you are not an engineer if you cannot invert a binary tree on a whiteboard. Both sides are a little right and mostly loud. Let me give the boring answer with examples. Where DSA showed up in real work A nightly job deduplicating 2 million customer records with List.contains() inside a…

19

  • Sam Whitaker
    DSA is useful. I use binary search every time I git bisect which commit broke prod. which is weekly.
    1 reply
  • Dana Kowalski
    The interview is a lossy proxy. Everyone in this thread is arguing about how lossy. That's the actual disagreement, and nobody has data.
Nikhil Sharan684
t/interview_horror

Good system design mock to watch before your first HLD round. Notice how long he stays on requirements and scale before drawing a single box. That is not wasting time, that is the interview. Watch it once normally, then again and pause before every answer.

6

  • Kenji Tanabe
    Agree on requirements. I've been on both sides of maybe 200 of these. The candidates who fail usually start drawing boxes in minute two. The ones who pass ask how many submissions per second arrive when a contest starts, because that spike is the real problem in a LeetCode design.
    1 reply
Nikhil Sharan2.2K
t/interview_horror3 min

Monotonic stack, explained with a queue at a chai stall

Problem: for every element in an array, find the first element to its right that is greater than it. If none, -1. Brute force: for each i, scan right until you find something bigger. O(n²). With n = 10^5 you are done for. The chai stall Imagine people standing in a line outside a chai stall, all looking to the right. Each person wants to know: who is the first person to my right who is taller than me? Walk along the…

Monotonic stack, explained with a queue at a chai stall
8

  • Trần Phương Thảo
    the dry run list is so helpful. I am QA not dev but I followed every step. thank you
Nikhil Sharan728
t/desi_devs2 min

To the tier-3 student who messaged me at 2:14 am

Last night at 2:14 am I got a long message from a third year student. Small private college, "koi company nahi aati", 90 questions done on LeetCode, and one line that I have not been able to stop thinking about: "bhaiya kya mera kuch nahi ho sakta?" I replied to him directly, but I get some version of this message every week, so I am writing the answer here once. First, about me, because people assume things. I did…

9

  • Karthikeyan S
    Adding one more door for tier-3 folks: embedded and electronics companies care way less about college name and way more about whether you can read a datasheet. Fewer people apply too
    1 reply
Nikhil Sharan1K
t/desi_devs4 min

Two pointers is not one trick. It is three shapes.

Every week someone messages me "bhaiya two pointers samajh aata hai but question mein apply nahi hota". That happens because people learn it as one trick. It is actually three different shapes, and the problem statement tells you which shape it wants if you read it slowly. Shape 1: opposite ends, moving inward Signal: the array is sorted (or you are allowed to sort it) and you want a pair with some property. Classic…

9

  • Karthikeyan S
    Shape 2 is basically how we drop bad samples from a ring buffer in firmware without allocating anything. Zero extra memory, very embedded friendly. Good post

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