How to use

buildTree

method

in

it.unimi.dsi.compression.TreeDecoder

/** Creates a new codeword-based decoder starting from a set
 * of complete, lexicographically ordered codewords. It
 * is responsability of the caller that the tree is well-formed,
 * that is, that the provided codewords are exactly the root-to-leaf
 * paths of such a tree.
 * 
 * @param lexSortedCodeWord a vector of lexically sorted codeWords.
 * @param symbol a mapping from codewords to symbols.
 */
public TreeDecoder( BitVector[] lexSortedCodeWord, int[] symbol ) {
  this( buildTree( lexSortedCodeWord, symbol, 0, 0, lexSortedCodeWord.length ), lexSortedCodeWord.length );
}

/** Creates a new codeword-based decoder starting from a set
 * of complete, lexicographically ordered codewords. It
 * is responsibility of the caller that the tree is well-formed,
 * that is, that the provided codewords are exactly the root-to-leaf
 * paths of such a tree.
 *
 * @param lexSortedCodeWord a vector of lexically sorted codeWords.
 * @param symbol a mapping from codewords to symbols.
 */
public TreeDecoder(BitVector[] lexSortedCodeWord, int[] symbol) {
  this(buildTree(lexSortedCodeWord, symbol, 0, 0, lexSortedCodeWord.length), lexSortedCodeWord.length);
}

/** Creates a new codeword-based decoder starting from a set
 * of complete, lexicographically ordered codewords. It
 * is responsability of the caller that the tree is well-formed,
 * that is, that the provided codewords are exactly the root-to-leaf
 * paths of such a tree.
 * 
 * @param lexSortedCodeWord a vector of lexically sorted codeWords.
 * @param symbol a mapping from codewords to symbols.
 */
public TreeDecoder( BitVector[] lexSortedCodeWord, int[] symbol ) {
  this( buildTree( lexSortedCodeWord, symbol, 0, 0, lexSortedCodeWord.length ), lexSortedCodeWord.length );
}

private static Node buildTree(BitVector lexSortedCodeWords[], final int[] symbol, int prefix, int offset, int length) {
  if (DEBUG) {
    System.err.println("****** " + offset + " " + length);
    System.err.println(Arrays.toString(lexSortedCodeWords));
    for(int i = 0; i < length; i++) {
      System.err.print(lexSortedCodeWords[offset + i].length() + "\t");
      for(int j = 0; j < lexSortedCodeWords[offset + i].length(); j++) System.err.print(lexSortedCodeWords[offset + i].getBoolean(j) ? 1 : 0);
      System.err.println();
    }
  }
  if (length == 1) return new LeafNode(symbol[offset]);
  for(int i = length - 1; i-- != 0;)
    if (lexSortedCodeWords[offset + i].getBoolean(prefix) != lexSortedCodeWords[offset + i + 1].getBoolean(prefix)) {
      final Node node = new Node();
      node.left = buildTree(lexSortedCodeWords, symbol, prefix + 1, offset, i + 1);
      node.right = buildTree(lexSortedCodeWords, symbol, prefix + 1, offset + i + 1, length - i - 1);
      return node;
    }
  throw new IllegalStateException();
}

private static Node buildTree( BitVector lexSortedCodeWords[], final int[] symbol, int prefix, int offset, int length ) {
  if ( DEBUG ) {
    System.err.println( "****** " + offset + " " + length ); 
    System.err.println( Arrays.toString( lexSortedCodeWords ) );
    for( int i = 0; i < length; i++ ) {
      System.err.print( lexSortedCodeWords[ offset + i ].size() + "\t" );
      for( int j = 0; j < lexSortedCodeWords[ offset + i ].size(); j++ ) System.err.print( lexSortedCodeWords[ offset + i ].getBoolean( j ) ? 1 : 0 );
      System.err.println();
    }
  }
  
  if ( length == 1 ) return new LeafNode( symbol[ offset ] );
  for( int i = length - 1; i-- != 0; ) 
    if ( lexSortedCodeWords[ offset + i ].get( prefix ) != lexSortedCodeWords[ offset + i + 1 ].get( prefix ) ) {
      final Node node = new Node();
      node.left = buildTree( lexSortedCodeWords, symbol, prefix + 1, offset, i + 1 );
      node.right = buildTree( lexSortedCodeWords, symbol, prefix + 1, offset + i + 1, length - i - 1 );
      return node;
    }
  
  throw new IllegalStateException();
}

private static Node buildTree( BitVector lexSortedCodeWords[], final int[] symbol, int prefix, int offset, int length ) {
  if ( DEBUG ) {
    System.err.println( "****** " + offset + " " + length ); 
    System.err.println( Arrays.toString( lexSortedCodeWords ) );
    for( int i = 0; i < length; i++ ) {
      System.err.print( lexSortedCodeWords[ offset + i ].size() + "\t" );
      for( int j = 0; j < lexSortedCodeWords[ offset + i ].size(); j++ ) System.err.print( lexSortedCodeWords[ offset + i ].getBoolean( j ) ? 1 : 0 );
      System.err.println();
    }
  }
  
  if ( length == 1 ) return new LeafNode( symbol[ offset ] );
  for( int i = length - 1; i-- != 0; ) 
    if ( lexSortedCodeWords[ offset + i ].get( prefix ) != lexSortedCodeWords[ offset + i + 1 ].get( prefix ) ) {
      final Node node = new Node();
      node.left = buildTree( lexSortedCodeWords, symbol, prefix + 1, offset, i + 1 );
      node.right = buildTree( lexSortedCodeWords, symbol, prefix + 1, offset + i + 1, length - i - 1 );
      return node;
    }
  
  throw new IllegalStateException();
}