PatriciaTrie Contribution

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This is a contribution of LimeWire's PatriciaTrie, as discussed at: 
http://groups.google.com/group/google-
guice/browse_frm/thread/ffb2a3b3b9e39e79?tvc=1 .

The files can be licensed as necessary (we own the copyright and can 
change/transfer the license).  I'm not sure what license, if any, these 
would need to be for inclusion.

Original issue reported on code.google.com by sberlin on 24 Sep 2007 at 6:12

Attachments:

• patricia.zip

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thanks!

It would be really, really (really) helpful if we could collect, here, a good 
variety
of use cases for this trie.

Original comment by kevin...@gmail.com on 1 Oct 2007 at 7:51

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We use it internally for a few cases.
 1) An IP list.  We have a KeyAnalyzer that analyzes ip addresses to store them 
(and/or ranges of them) as compactly as possible.  See: 
https://www.limewire.org/fisheye/browse/~raw,r=1.18/limecvs/core/com/limegroup/g
nutel
la/filters/IPList.java . 

 2) Storing a Kademlia DHT's internal structure.  This is probably a very specific 
use-case, although it works very well. :)

Other use cases:
 3) A very efficient (both in memory & CPU) dictionary.  It could be used for 
something like a cellphone's phonebook.  You start typing and it immediately 
finds 
all strings that began with your string.  At the same time the structure acts 
like a 
Map preventing you from adding the same String twice.  It's kind of like a 
super-
SortedMap.

I'm sure there's a ton of other cases, but those are the ones we use (and have 
plans 
to use).  The really awesome things about Patricia is the way it does lookups.  
Consider the IPList -- IPv4 addresses have a fixed size of 32 bits.  So no 
matter 
how many items you have stored in the Trie, it will always do at most 32 bit 
comparisons.  And it will often do less (because it intelligently traverses the 
tree), and it will keep things sorted and tell you all addresses that begin 
with 
X.Y, etc...  

Original comment by sberlin on 1 Oct 2007 at 8:10

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Great stuff, folks.  Thanks so much.

With the sheer mountain of work involved in getting our existing stuff 
polished, I'm
afraid it may be some time before I can look at breaking into new territory. 
But, I
do think that this trie and tries in general are a very promising addition, so 
don't
lose hope!

Original comment by kevin...@gmail.com on 16 Oct 2007 at 3:37

• Changed state: Accepted

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Disclaimer: I don't know much about Tries.

I can imagine that many use cases for a Trie break into at least two categories

1. The SortedMap/NavigableMap the right API abstraction that the caller wants, 
but
due to the nature of the data, a Trie can be much faster than existing
implementations of these interfaces.

2. What the caller wants to see doesn't look like a Map at all, but something 
much
simpler that deals only with prefix-matching like (rough guess):

  public interface Trie<N, V> {
    boolean containsMatch(List<? extends N> sequence);
    V get(List<? extends N> sequence); // doesn't require exact match
    void put(List<? extends N> sequencePrefix, V value);
  }

A separate issue: should we consider providing an alternate interface that is
tailored to character-based tries, so this alternate API could use CharSequence 
in
place of List<Character>?  Then there would be two simple methods
Tries.asCharacterTrie() and Tries.forCharacterTrie() to go back and forth 
between the
two.

Original comment by kevin...@gmail.com on 23 Oct 2007 at 4:29

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From my experience, #1 is exactly right.  A Trie easily doubles as a 
super-efficient 
SortedMap/NavigableMap.

You hit the nail on #2 with the CharSequence version.  Trie's I've encountered 
function with a similar interface, but tailored towards the combined sequence 
instead of the pieces that build up the sequence.  That is, the methods would 
look 
like:

   public interface Trie<K, V> {
      boolean hasPrefix(K prefix);
      SortedMap<K, V> getPrefixedBy(K prefix); // returns a view over all entries 
prefixed by K
      void put(K key, V value);
   }

The difference is the Trie is directly acting off a K value, which would be the 
CharSequence to a Character, or a NumberSequence to a Number.  This has the 
advantage of being able to reuse the interface for arbitrary-length keys or 
fixed-
length keys whose contents don't divide easily into objects.  (For example, IP 
addresses being composed of bits, CharSequences, phone numbers, etc...)

The Trie interface in the submission includes a few additional convenience 
methods 
and directly subclasses SortedMap (if it were targetted for 1.6, it would 
extend 
NavigableMap too).  The additions are for better use with fixed-size keys and 
being 
able to visit the entries in the map while traversing (with a 'Cursor').

Original comment by sberlin on 23 Oct 2007 at 5:49

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(Really, that getPrefixedBy could just return a List<V> - having it return a vw 
of 
the map itself enables some really cool things.)

Original comment by sberlin on 23 Oct 2007 at 5:50

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Original comment by kevin...@gmail.com on 3 Nov 2007 at 5:32

• Added labels: Post-1.0

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Original comment by kevin...@gmail.com on 2 Jun 2008 at 5:48

• Removed labels: Post-1.0

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Hello,

currently I'm wirting something for my studies and did a bit of research about 
Tries.
I fall upon a Hash Table performance like Trie called HAT-Trie.
It's a proposal for a fast memory aware Trie that can deal with non equal 
memory costs.
http://crpit.com/confpapers/CRPITV62Askitis.pdf

In my opinion it maybe would be a great advantage to use this Trie.

Hope I could help,
Tim

Original comment by tim.frey...@googlemail.com on 22 Mar 2009 at 10:31

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To completely generalize it, a Trie is kind of a particular way of representing 
a
  Set< List< E > >
or, easily enough, a
  Map< List< E >, V >
where E is typically a character (List<E> is a String). The representation 
allows
certain specific operations to be very efficient, and is efficient for storage 
when
there are many common prefixes among the List<E> (a spelling dictionary, for 
example).

There may be some benefit to completely abstracting it in this way, although
translating the common use case of a String key would be an excessive amount of 
overhead.

Original comment by ray.a.co...@gmail.com on 3 Aug 2009 at 5:53

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As a use case, I've used it for finding phrases within a large text document. I 
have
some set of phrases that I'm looking for (not Strings, but sequences of words, 
hence
- List<String>) stored as a Trie. To search, I walk the normalized text (split 
on
whitespace, punctuation removed, handle case insensitivity, etc.) which is also 
a
List<String>, keeping track of possible matches as I go.

Generalizing, this is finding all possible subsequences of List<E> (the text) 
that
are members of a given Set<List<E>> (the search phrases).

The big benefit is that the text, which can be very large, only needs to be 
traversed
once to find any one (or all) of thousands of possible phrases. It scales very 
well.

Original comment by ray.a.co...@gmail.com on 3 Aug 2009 at 6:05

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I have the same use case as Ray.a.conner, and I'd also use it for scalable 
tab|auto-
completion in interactive consoles|text fields.

Original comment by cresw...@gmail.com on 3 Aug 2009 at 6:31

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Are you folks using the attached PatriciaTrie implementation, or a separate one?

Original comment by sberlin on 3 Aug 2009 at 6:34

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The Google code base includes multiple Java trie implementations. If we chose 
to add
a trie to the library, we'd probably start with one of those.

Original comment by jared.l....@gmail.com on 3 Aug 2009 at 6:44

• Added labels: Type-Enhancement
• Removed labels: Type-Defect

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I rolled my own implementation, some years ago. I wasn't storing simple 
strings, and
pretty much everything out there was character-centric. Once I made the 
abstraction
to sequences of strings, sequences of objects was a no-brainer. Although I never
needed to implement many of the Trie operations that others find useful; I only
needed sub-sequence matching.

Original comment by ray.a.co...@gmail.com on 3 Aug 2009 at 8:13

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Original comment by kevin...@gmail.com on 17 Sep 2009 at 6:02

• Added labels: Milestone-Post1.0

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Original comment by master.j...@gmail.com on 24 Nov 2009 at 8:06

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Moved to http://code.google.com/p/guava-libraries/issues/detail?id=10

Original comment by kevinb@google.com on 5 Jan 2010 at 11:10

• Changed state: Moved

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i want linked list implementation of trie datastructure can you suggest  

Original comment by chaith...@gmail.com on 19 Mar 2010 at 1:48

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Hi, tim.frey.online. Do you have an implementation of HAT-trie?

Original comment by tiberiut...@gmail.com on 20 Jun 2010 at 7:49