Re: startsWith datastructure

Robert Klemme <>
Sat, 27 Oct 2012 13:56:06 +0200
On 27.10.2012 12:50, Roedy Green wrote:

Lets say you had a list of book publishers and the block of ISBN
numbers they own. e.g. Prentice-Hall owns all isbns of the form
or put another way, own all ISBNs that startsWith "013".
Some publishers such as O'Reilly own multiple blocks.

      013, Prentice Hall
      014, Penguin
     0201, Addison-Wesley
     0393, H. W. Norton
     0471, John Wiley & Sons
     0553, Bantam
   059600, O'Reilly
   156592, O'Reilly
     0060, Harper
    06723, Sams
    07356, Microsoft Press
    07432, Simon & Schuster
    07710, McClelland & Stewart
    08125, Tor
   086571, New Society Publishers
  0915972, Love Line
15795106, Ronin Publishing


Your list is incomplete. It has only the major publishers.

The problem is, given an ISBN, can you make at guess at its publisher?

What sort of datastructure/lookup mechanism would you use?

Obviously, you could just do a linear search looking for a match, and
unless the list got very long, that should suffice, but, just for
fun, say you wanted something faster, what would you do?

This is just an example of a class of problem I wanted to write a
little essay on for the Java glossary with possible solutions.

That's a typical use case for a Trie:

Other than that you could use a TreeSet and make use of method subSet()
where the lower bound is the fragment you got and the upper bound is the
fragment with the last character increased "by one" or a "max" character

Or you use a sorted array and use Arrays.binarySearch(). The Trie is
more efficient though.



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