Voxer Java Developer interview questions

The task was to build a command line utility to search for string. The input is text file (where every line is a new string) and some prefix. The program should print the shortest word in a text file that starts with the given prefix. The main idea was to build a perfect data structure to store the strings from text file and to make a look up. It is supposed that text file could be very big and looking for a string in a set of strings is not suitable.