It is my favorite algorithm called array quadruplet. I did talk about the analysis of the algorithm and then wrote down the algorithm without any bug and pass all test cases first time. Only thing I did is to include library using ..., I explained to the peer that I have worked on the algorithm multiple times, but one time a young lady who was preparing facebook onsite, she told me that I should simplify the code to check if dictionary contains key or not. So I only need to write three lines of code from line 57 to line 62, before I need to write if/ else and then update list in both cases.
Here is my C# code.