Lucene example source code file (TernaryTree.java)

This example Lucene source code file (TernaryTree.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

block_size, charvector, charvector, io, item, item, iterator, object, override, stack, string, string, stringbuilder, ternarytree, ternarytree, util

The Lucene TernaryTree.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.analysis.compound.hyphenation;

import java.util.Enumeration;
import java.util.Stack;
import java.io.Serializable;

/**
 * <h2>Ternary Search Tree.
 * 
 * <p>
 * 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).
 * </p>
 * 
 * <p>
 * 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.
 * </p>
 * 
 * <p>
 * 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.
 * </p>
 * 
 * This class has been taken from the Apache FOP project (http://xmlgraphics.apache.org/fop/). They have been slightly modified. 
 */

public class TernaryTree implements Cloneable, Serializable {

  /**
   * We use 4 arrays to represent a node. I guess I should have created a proper
   * node class, but somehow Knuth's pascal code made me forget we now have a
   * portable language with virtual memory management and automatic garbage
   * collection! And now is kind of late, furthermore, if it ain't broken, don't
   * fix it.
   */

  /**
   * 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!
   */
  protected char[] lo;

  /**
   * Pointer to high branch.
   */
  protected char[] hi;

  /**
   * Pointer to equal branch and to data when this node is a string terminator.
   */
  protected char[] eq;

  /**
   * <P>
   * The character stored in this node: splitchar. Two special values are
   * reserved:
   * </P>
   * <ul>
   * <li>0x0000 as string terminator
   * <li>0xFFFF to indicate that the branch starting at this node is compressed
   * </ul>
   * <p>
   * This shouldn't be a problem if we give the usual semantics to strings since
   * 0xFFFF is guaranteed not to be an Unicode character.
   * </p>
   */
  protected char[] sc;

  /**
   * This vector holds the trailing of the keys when the branch is compressed.
   */
  protected CharVector kv;

  protected char root;

  protected char freenode;

  protected int length; // number of items in tree

  protected static final int BLOCK_SIZE = 2048; // allocation size for arrays

  TernaryTree() {
    init();
  }

  protected void init() {
    root = 0;
    freenode = 1;
    length = 0;
    lo = new char[BLOCK_SIZE];
    hi = new char[BLOCK_SIZE];
    eq = new char[BLOCK_SIZE];
    sc = new char[BLOCK_SIZE];
    kv = new CharVector();
  }

  /**
   * 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.
   */
  public void insert(String key, char val) {
    // make sure we have enough room in the arrays
    int len = key.length() + 1; // maximum number of nodes that may be generated
    if (freenode + len > eq.length) {
      redimNodeArrays(eq.length + BLOCK_SIZE);
    }
    char strkey[] = new char[len--];
    key.getChars(0, len, strkey, 0);
    strkey[len] = 0;
    root = insert(root, strkey, 0, val);
  }

  public void insert(char[] key, int start, char val) {
    int len = strlen(key) + 1;
    if (freenode + len > eq.length) {
      redimNodeArrays(eq.length + BLOCK_SIZE);
    }
    root = insert(root, key, start, val);
  }

  /**
   * The actual insertion function, recursive version.
   */
  private char insert(char p, char[] key, int start, char val) {
    int len = strlen(key, start);
    if (p == 0) {
      // this means there is no branch, this node will start a new branch.
      // Instead of doing that, we store the key somewhere else and create
      // only one node with a pointer to the key
      p = freenode++;
      eq[p] = val; // holds data
      length++;
      hi[p] = 0;
      if (len > 0) {
        sc[p] = 0xFFFF; // indicates branch is compressed
        lo[p] = (char) kv.alloc(len + 1); // use 'lo' to hold pointer to key
        strcpy(kv.getArray(), lo[p], key, start);
      } else {
        sc[p] = 0;
        lo[p] = 0;
      }
      return p;
    }

    if (sc[p] == 0xFFFF) {
      // branch is compressed: need to decompress
      // this will generate garbage in the external key array
      // but we can do some garbage collection later
      char pp = freenode++;
      lo[pp] = lo[p]; // previous pointer to key
      eq[pp] = eq[p]; // previous pointer to data
      lo[p] = 0;
      if (len > 0) {
        sc[p] = kv.get(lo[pp]);
        eq[p] = pp;
        lo[pp]++;
        if (kv.get(lo[pp]) == 0) {
          // key completly decompressed leaving garbage in key array
          lo[pp] = 0;
          sc[pp] = 0;
          hi[pp] = 0;
        } else {
          // we only got first char of key, rest is still there
          sc[pp] = 0xFFFF;
        }
      } else {
        // In this case we can save a node by swapping the new node
        // with the compressed node
        sc[pp] = 0xFFFF;
        hi[p] = pp;
        sc[p] = 0;
        eq[p] = val;
        length++;
        return p;
      }
    }
    char s = key[start];
    if (s < sc[p]) {
      lo[p] = insert(lo[p], key, start, val);
    } else if (s == sc[p]) {
      if (s != 0) {
        eq[p] = insert(eq[p], key, start + 1, val);
      } else {
        // key already in tree, overwrite data
        eq[p] = val;
      }
    } else {
      hi[p] = insert(hi[p], key, start, val);
    }
    return p;
  }

  /**
   * Compares 2 null terminated char arrays
   */
  public static int strcmp(char[] a, int startA, char[] b, int startB) {
    for (; a[startA] == b[startB]; startA++, startB++) {
      if (a[startA] == 0) {
        return 0;
      }
    }
    return a[startA] - b[startB];
  }

  /**
   * Compares a string with null terminated char array
   */
  public static int strcmp(String str, char[] a, int start) {
    int i, d, len = str.length();
    for (i = 0; i < len; i++) {
      d = (int) str.charAt(i) - a[start + i];
      if (d != 0) {
        return d;
      }
      if (a[start + i] == 0) {
        return d;
      }
    }
    if (a[start + i] != 0) {
      return -a[start + i];
    }
    return 0;

  }

  public static void strcpy(char[] dst, int di, char[] src, int si) {
    while (src[si] != 0) {
      dst[di++] = src[si++];
    }
    dst[di] = 0;
  }

  public static int strlen(char[] a, int start) {
    int len = 0;
    for (int i = start; i < a.length && a[i] != 0; i++) {
      len++;
    }
    return len;
  }

  public static int strlen(char[] a) {
    return strlen(a, 0);
  }

  public int find(String key) {
    int len = key.length();
    char strkey[] = new char[len + 1];
    key.getChars(0, len, strkey, 0);
    strkey[len] = 0;

    return find(strkey, 0);
  }

  public int find(char[] key, int start) {
    int d;
    char p = root;
    int i = start;
    char c;

    while (p != 0) {
      if (sc[p] == 0xFFFF) {
        if (strcmp(key, i, kv.getArray(), lo[p]) == 0) {
          return eq[p];
        } else {
          return -1;
        }
      }
      c = key[i];
      d = c - sc[p];
      if (d == 0) {
        if (c == 0) {
          return eq[p];
        }
        i++;
        p = eq[p];
      } else if (d < 0) {
        p = lo[p];
      } else {
        p = hi[p];
      }
    }
    return -1;
  }

  public boolean knows(String key) {
    return (find(key) >= 0);
  }

  // redimension the arrays
  private void redimNodeArrays(int newsize) {
    int len = newsize < lo.length ? newsize : lo.length;
    char[] na = new char[newsize];
    System.arraycopy(lo, 0, na, 0, len);
    lo = na;
    na = new char[newsize];
    System.arraycopy(hi, 0, na, 0, len);
    hi = na;
    na = new char[newsize];
    System.arraycopy(eq, 0, na, 0, len);
    eq = na;
    na = new char[newsize];
    System.arraycopy(sc, 0, na, 0, len);
    sc = na;
  }

  public int size() {
    return length;
  }

  @Override
  public Object clone() {
    TernaryTree t = new TernaryTree();
    t.lo = this.lo.clone();
    t.hi = this.hi.clone();
    t.eq = this.eq.clone();
    t.sc = this.sc.clone();
    t.kv = (CharVector) this.kv.clone();
    t.root = this.root;
    t.freenode = this.freenode;
    t.length = this.length;

    return t;
  }

  /**
   * 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.
   */
  protected void insertBalanced(String[] k, char[] v, int offset, int n) {
    int m;
    if (n < 1) {
      return;
    }
    m = n >> 1;

    insert(k[m + offset], v[m + offset]);
    insertBalanced(k, v, offset, m);

    insertBalanced(k, v, offset + m + 1, n - m - 1);
  }

  /**
   * Balance the tree for best search performance
   */
  public void balance() {
    // System.out.print("Before root splitchar = ");
    // System.out.println(sc[root]);

    int i = 0, n = length;
    String[] k = new String[n];
    char[] v = new char[n];
    Iterator iter = new Iterator();
    while (iter.hasMoreElements()) {
      v[i] = iter.getValue();
      k[i++] = iter.nextElement();
    }
    init();
    insertBalanced(k, v, 0, n);

    // With uniform letter distribution sc[root] should be around 'm'
    // System.out.print("After root splitchar = ");
    // System.out.println(sc[root]);
  }

  /**
   * 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!).
   * 
   */
  public void trimToSize() {
    // first balance the tree for best performance
    balance();

    // redimension the node arrays
    redimNodeArrays(freenode);

    // ok, compact kv array
    CharVector kx = new CharVector();
    kx.alloc(1);
    TernaryTree map = new TernaryTree();
    compact(kx, map, root);
    kv = kx;
    kv.trimToSize();
  }

  private void compact(CharVector kx, TernaryTree map, char p) {
    int k;
    if (p == 0) {
      return;
    }
    if (sc[p] == 0xFFFF) {
      k = map.find(kv.getArray(), lo[p]);
      if (k < 0) {
        k = kx.alloc(strlen(kv.getArray(), lo[p]) + 1);
        strcpy(kx.getArray(), k, kv.getArray(), lo[p]);
        map.insert(kx.getArray(), k, (char) k);
      }
      lo[p] = (char) k;
    } else {
      compact(kx, map, lo[p]);
      if (sc[p] != 0) {
        compact(kx, map, eq[p]);
      }
      compact(kx, map, hi[p]);
    }
  }

  public Enumeration<String> keys() {
    return new Iterator();
  }

  public class Iterator implements Enumeration<String> {

    /**
     * current node index
     */
    int cur;

    /**
     * current key
     */
    String curkey;

    private class Item implements Cloneable {
      char parent;

      char child;

      public Item() {
        parent = 0;
        child = 0;
      }

      public Item(char p, char c) {
        parent = p;
        child = c;
      }

      @Override
      public Object clone() {
        return new Item(parent, child);
      }

    }

    /**
     * Node stack
     */
    Stack<Item> ns;

    /**
     * key stack implemented with a StringBuilder
     */
    StringBuilder ks;

    public Iterator() {
      cur = -1;
      ns = new Stack<Item>();
      ks = new StringBuilder();
      rewind();
    }

    public void rewind() {
      ns.removeAllElements();
      ks.setLength(0);
      cur = root;
      run();
    }

    public String nextElement() {
      String res = new String(curkey);
      cur = up();
      run();
      return res;
    }

    public char getValue() {
      if (cur >= 0) {
        return eq[cur];
      }
      return 0;
    }

    public boolean hasMoreElements() {
      return (cur != -1);
    }

    /**
     * traverse upwards
     */
    private int up() {
      Item i = new Item();
      int res = 0;

      if (ns.empty()) {
        return -1;
      }

      if (cur != 0 && sc[cur] == 0) {
        return lo[cur];
      }

      boolean climb = true;

      while (climb) {
        i = ns.pop();
        i.child++;
        switch (i.child) {
          case 1:
            if (sc[i.parent] != 0) {
              res = eq[i.parent];
              ns.push((Item) i.clone());
              ks.append(sc[i.parent]);
            } else {
              i.child++;
              ns.push((Item) i.clone());
              res = hi[i.parent];
            }
            climb = false;
            break;

          case 2:
            res = hi[i.parent];
            ns.push((Item) i.clone());
            if (ks.length() > 0) {
              ks.setLength(ks.length() - 1); // pop
            }
            climb = false;
            break;

          default:
            if (ns.empty()) {
              return -1;
            }
            climb = true;
            break;
        }
      }
      return res;
    }

    /**
     * traverse the tree to find next key
     */
    private int run() {
      if (cur == -1) {
        return -1;
      }

      boolean leaf = false;
      while (true) {
        // first go down on low branch until leaf or compressed branch
        while (cur != 0) {
          if (sc[cur] == 0xFFFF) {
            leaf = true;
            break;
          }
          ns.push(new Item((char) cur, '\u0000'));
          if (sc[cur] == 0) {
            leaf = true;
            break;
          }
          cur = lo[cur];
        }
        if (leaf) {
          break;
        }
        // nothing found, go up one node and try again
        cur = up();
        if (cur == -1) {
          return -1;
        }
      }
      // The current node should be a data node and
      // the key should be in the key stack (at least partially)
      StringBuilder buf = new StringBuilder(ks.toString());
      if (sc[cur] == 0xFFFF) {
        int p = lo[cur];
        while (kv.get(p) != 0) {
          buf.append(kv.get(p++));
        }
      }
      curkey = buf.toString();
      return 0;
    }

  }

  public void printStats() {
    System.out.println("Number of keys = " + Integer.toString(length));
    System.out.println("Node count = " + Integer.toString(freenode));
    // System.out.println("Array length = " + Integer.toString(eq.length));
    System.out.println("Key Array length = " + Integer.toString(kv.length()));

    /*
     * for(int i=0; i<kv.length(); i++) if ( kv.get(i) != 0 )
     * System.out.print(kv.get(i)); else System.out.println("");
     * System.out.println("Keys:"); for(Enumeration enum = keys();
     * enum.hasMoreElements(); ) System.out.println(enum.nextElement());
     */

  }

  public static void main(String[] args) throws Exception {
    TernaryTree tt = new TernaryTree();
    tt.insert("Carlos", 'C');
    tt.insert("Car", 'r');
    tt.insert("palos", 'l');
    tt.insert("pa", 'p');
    tt.trimToSize();
    System.out.println((char) tt.find("Car"));
    System.out.println((char) tt.find("Carlos"));
    System.out.println((char) tt.find("alto"));
    tt.printStats();
  }

}