ZOJ Problem Set - 1825
You are to find all the two-word compound words in a dictionary. A two-word compound word is a word in the dictionary that is the concatenation of exactly two other words in the dictionary.
Standard input consists of a number of lowercase words, one per line, in alphabetical order. There will be no more than 120,000 words.
Your output should contain all the compound words, one per line, in alphabetical order.
Source: University of Waterloo Local Contest 1996.09.28