Status: 15+ yrs S/W exp
Position: Senior Developer

Sharing my interviewing experience with Facebook for a Senior Dev role. I had a technical the phonescreen and was rejected. I was asked 2 questions.

https://leetcode.com/problems/toeplitz-matrix/
The other question was about adding 2 numbers with decimal point provided in the form of a string. For e.g. "12.345" + "5.05"

I answered the first question in Time=O(m*n) m and n being matrix dimensions and constant space
I answered the second question in Time=O(n) , n being length of larger input string with O(n) extra space.

At the end of the interview, I had a feeling that I had answered the questions pretty well and the interviewer looked very satisfied. There was even time left to chit-chat after I had answered both the questions.

Obviously I was very heartbroken when I heard about the result which was given to me within hours of the interview completion. I am still perplexed as to what went wrong. Ok, maybe I could have written a more space optimal solution for the second question O(1) instead of O(n). And in the first one, I could have made it simpler in code but in any case the solution I wrote was optimal in terms if time and space and I coded it up in the stipulated amout of time.

I am still perplexed about the final outcome.