So, to restate your problem, you are looking to match between zero and length - hint_length arbitrary characters, the hint and between zero and length - hint_length arbitrary characters. The perlre sign for "between zero and infinity" is *, though you can be more specific (hint: look for the bit about curly braces in the doc link). Good luck -- old-hand at semester end cramming recommends starting earlier next time ;-).
The intelligent reader will judge for himself. Without examining the facts fully and fairly, there is no way of knowing whether vox populi is really vox dei, or merely vox asinorum. — Cyrus H. Gordon