Prefix free codes. In data compression, a set of binary strings is prefix free if no string is a prefix of another. For example, {01,10,0010,1111} is prefix free, but {01,10,0010,10100} is not because 10 is a prefix of 10100. Design an efficient algorithm to determine if a set of binary strings is prefix-free. The running time of your algorithm should be proportional the number of bits in all of the binary stings.

Boggle. Boggle is a word game played on an $4$-by-$4$ grid of tiles, where each tile contains one letter in the alphabet. The goal is to find all words in the dictionary that can be made by following a path of adjacent tiles (with no tile repeated), where two tiles are adjacent if they are horizontal, vertical, or diagonal neighbors.

Suffix trees. Learn about and implement suffix trees, the ultimate string searching data structure.