Class TernaryTree

Ternary Search Tree.

A ternary search tree is a hybrid between a binary tree and a digital search tree (trie). Keys are limited to strings. A data value of type char is stored in each leaf node. It can be used as an index (or pointer) to the data. Branches that only contain one key are compressed to one node by storing a pointer to the trailer substring of the key. This class is intended to serve as base class or helper class to implement Dictionary collections or the like. Ternary trees have some nice properties as the following: the tree can be traversed in sorted order, partial matches (wildcard) can be implemented, retrieval of all keys within a given distance from the target, etc. The storage requirements are higher than a binary tree but a lot less than a trie. Performance is comparable with a hash table, sometimes it outperforms a hash function (most of the time can determine a miss faster than a hash).

The main purpose of this java port is to serve as a base for implementing TeX's hyphenation algorithm (see The TeXBook, appendix H). Each language requires from 5000 to 15000 hyphenation patterns which will be keys in this tree. The strings patterns are usually small (from 2 to 5 characters), but each char in the tree is stored in a node. Thus memory usage is the main concern. We will sacrifice 'elegance' to keep memory requirements to the minimum. Using java's char type as pointer (yes, I know pointer it is a forbidden word in java) we can keep the size of the node to be just 8 bytes (3 pointers and the data char). This gives room for about 65000 nodes. In my tests the english patterns took 7694 nodes and the german patterns 10055 nodes, so I think we are safe.

All said, this is a map with strings as keys and char as value. Pretty limited!. It can be extended to a general map by using the string representation of an object and using the char value as an index to an array that contains the object values.

This class has been taken from the Apache FOP project (http://xmlgraphics.apache.org/fop/). They have been slightly modified.

Inheritance

System.Object

TernaryTree

HyphenationTree

Namespace: Lucene.Net.Analysis.Compound.Hyphenation

Assembly: Lucene.Net.Analysis.Common.dll

Syntax

public class TernaryTree : object

Fields

BLOCK_SIZE

Declaration

protected const int BLOCK_SIZE = null

Field Value

Type	Description
System.Int32

m_eq

Pointer to equal branch and to data when this node is a string terminator.

Declaration

protected char[] m_eq

Field Value

Type	Description
System.Char[]

m_freenode

Declaration

protected char m_freenode

Field Value

Type	Description
System.Char

m_hi

Pointer to high branch.

Declaration

protected char[] m_hi

Field Value

Type	Description
System.Char[]

m_kv

This vector holds the trailing of the keys when the branch is compressed.

Declaration

protected CharVector m_kv

Field Value

Type	Description
CharVector

m_length

Declaration

protected int m_length

Field Value

Type	Description
System.Int32

m_lo

Pointer to low branch and to rest of the key when it is stored directly in this node, we don't have unions in java!

Declaration

protected char[] m_lo

Field Value

Type	Description
System.Char[]

m_root

Declaration

protected char m_root

Field Value

Type	Description
System.Char

m_sc

The character stored in this node: splitchar. Two special values are reserved:

• 0x0000 as string terminator
• 0xFFFF to indicate that the branch starting at this node is compressed

This shouldn't be a problem if we give the usual semantics to strings since 0xFFFF is guaranteed not to be an Unicode character.

Declaration

protected char[] m_sc

Field Value

Type	Description
System.Char[]

Properties

Length

Declaration

public virtual int Length { get; }

Property Value

Type	Description
System.Int32

Methods

Balance()

Balance the tree for best search performance

Declaration

public virtual void Balance()

Clone()

Declaration

public virtual object Clone()

Returns

Type	Description
System.Object

Find(Char[], Int32)

Declaration

public virtual int Find(char[] key, int start)

Parameters

Type	Name	Description
System.Char[]	key
System.Int32	start

Returns

Type	Description
System.Int32

Find(String)

Declaration

public virtual int Find(string key)

Parameters

Type	Name	Description
System.String	key

Returns

Type	Description
System.Int32

Init()

Declaration

protected virtual void Init()

Insert(Char[], Int32, Char)

Declaration

public virtual void Insert(char[] key, int start, char val)

Parameters

Type	Name	Description
System.Char[]	key
System.Int32	start
System.Char	val

Insert(String, Char)

Branches are initially compressed, needing one node per key plus the size of the string key. They are decompressed as needed when another key with same prefix is inserted. This saves a lot of space, specially for long keys.

Declaration

public virtual void Insert(string key, char val)

Parameters

Type	Name	Description
System.String	key
System.Char	val

InsertBalanced(String[], Char[], Int32, Int32)

Recursively insert the median first and then the median of the lower and upper halves, and so on in order to get a balanced tree. The array of keys is assumed to be sorted in ascending order.

Declaration

protected virtual void InsertBalanced(string[] k, char[] v, int offset, int n)

Parameters

Type	Name	Description
System.String[]	k
System.Char[]	v
System.Int32	offset
System.Int32	n

Keys()

Declaration

public virtual IEnumerator<string> Keys()

Returns

Type	Description
IEnumerator<System.String>

Knows(String)

Declaration

public virtual bool Knows(string key)

Parameters

Type	Name	Description
System.String	key

Returns

Type	Description
System.Boolean

PrintStats(TextWriter)

Declaration

public virtual void PrintStats(TextWriter out)

Parameters

Type	Name	Description
TextWriter	out

StrCmp(Char[], Int32, Char[], Int32)

Compares 2 null terminated char arrays

Declaration

public static int StrCmp(char[] a, int startA, char[] b, int startB)

Parameters

Type	Name	Description
System.Char[]	a
System.Int32	startA
System.Char[]	b
System.Int32	startB

Returns

Type	Description
System.Int32

StrCmp(String, Char[], Int32)

Compares a string with null terminated char array

Declaration

public static int StrCmp(string str, char[] a, int start)

Parameters

Type	Name	Description
System.String	str
System.Char[]	a
System.Int32	start

Returns

Type	Description
System.Int32

StrCpy(Char[], Int32, Char[], Int32)

Declaration

public static void StrCpy(char[] dst, int di, char[] src, int si)

Parameters

Type	Name	Description
System.Char[]	dst
System.Int32	di
System.Char[]	src
System.Int32	si

StrLen(Char[])

Declaration

public static int StrLen(char[] a)

Parameters

Type	Name	Description
System.Char[]	a

Returns

Type	Description
System.Int32

StrLen(Char[], Int32)

Declaration

public static int StrLen(char[] a, int start)

Parameters

Type	Name	Description
System.Char[]	a
System.Int32	start

Returns

Type	Description
System.Int32

TrimToSize()

Each node stores a character (splitchar) which is part of some key(s). In a compressed branch (one that only contain a single string key) the trailer of the key which is not already in nodes is stored externally in the kv array. As items are inserted, key substrings decrease. Some substrings may completely disappear when the whole branch is totally decompressed. The tree is traversed to find the key substrings actually used. In addition, duplicate substrings are removed using a map (implemented with a TernaryTree!).

Declaration

public virtual void TrimToSize()