Phone call with HR rep.

Then we scheduled an interview with the hiring team leader.

Good atmosphere in their offices.

In the technical questions stage of the interview, the TL pulled out a laptop and asked me to write running code in C (described below).

You have an already prepared function that converts %XY (where X and Y are hexadecimal) to ASCII characters (for instance, %65 = 'a').

Your program's input is a string that may include %XY. Convert it to a string in ASCII (without %XY).

Note that there could be an ASCII code for '%' in your string (%25 = '%'), and then you need to reconvert the result.