Alien Dictionary

The Problem There is a new alien language that uses the English alphabet. However, the order of the letters is unknown to you. You are given a list of strings words from the alien language’s dictionary. It is claimed that the strings in words are sorted lexicographically by the rules of this new language. A string a is lexicographically smaller than a string b if, in the first position where a and b differ, string a has a letter that appears earlier in the alien language than the corresponding letter in b. If the first min(a.length, b.length) characters do not differ, then the shorter string is the lexicographically smaller one. ...