[Need your help] Could you explain one of your solutions?

[JTOne123]

Hi @charles-wangkai, I hope you're doing well

If you have 10min, would you add a few comments for this solution?
https://github.com/charles-wangkai/hackerrank/blob/c418fb24e08e5c57a1bd0d91f95ab2af32f01c64/decibinary-numbers/Solution.java

I want to understand deeper buildF method and why do you use left-shift and why variable names are C, F, S?

PS:
(If you don't have time, just close this issue)
Sorry for this question and thank you!