Hi all
Here's my Wayfair interview experience for L4 Onsite

1. Behavioural - General questions, nothing too great. Went Okay.
2. Coding Round - Write an Api to count two arbitrarily large strings : I came up with an optimal solution. All ODTs passed. 1st Follow up - What if the input strings have commas and even the result should be decorated by commas - I modified my earlier APIs slightly to get the answer. Again, all ODTs passed without any issues. This was about 30 mins into the interview. 2nd Follow up - Implement Fibonacci using your Api : I implemented a naive, brute force and did mention that this would not be super efficient. It worked for all ODTs but for the Performance-Checking ODT. 3rd Follow up : By this time, the interviewer did mention that I was doing good...and just relax. I told him I could memoize the previous solution to bring down complexity from exponential to linear. Implemented it. Now, all ODTs passed. 4th Follow up - The memoized solution would take up much of memory, is there a better solutuon? This was like 7-8 mins left for the interview. I implemented bottom up DP, and this also passed all ODTs.
   By far, my best performance
3. System design - Tinyurl. I thought I did well here...read/write APIs, Estimates, NoSql store, Caching layer, Key-Generation Service....301/302 Http response codes, load balancer etc.
4. OOAD - Design a bike rental software. Was fine and engaging.

I got an offer, but was down-levelled to L3 because the System Deaign interviewer wasn't terribly impressed.