This is a very hard interview question, apparently asked during a number of Google and Amazon interviews. In my personal experience, I have asked this question to a number of people. Similar to me, only after providing a second hint to the question, have they been able to solve it.
How many hints do you need to solve this question? (add it to the comments)
The sequence presented is A, B, C, D, …
The “S” presents a straight line. “C” presents a curved line.
Since A has three “S”traight lines, it is represented by three S.
B has two “C”urved lines and one “S”traight line, therefore, SCC.
E, the next letter after D, is presented by 4 “S”traight lines.