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Programming Problem - Find Longest Word Made of Other Words

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Write a program that reads a file containing a sorted list of words (one

word per line, no spaces, all lower case), then identifies the longest

word in the file that can be constructed by concatenating copies of

shorter words also found in the file.

For example, if the file contained:

   cat

   cats

   catsdogcats

   catxdogcatsrat

   dog

   dogcatsdog

   hippopotamuses

   rat

   ratcatdogcat

The answer would be 'ratcatdogcat' - at 12 letters, it is the longest

word made up of other words in the list. The program should then

go on to report how many of the words in the list can be constructed

of other words in the list.

Performance matters: the program should return results

quickly even for very large lists (100,000+ items).

Please find attached a file, words.zip, containing a word list, words.txt,

with 173k rows, for testing purposes.