Package it.unimi.dsi.compression

Class HuTuckerCodec

  • All Implemented Interfaces:
    Codec, PrefixCodec, Serializable
    public class HuTuckerCodec
extends Object
implements PrefixCodec, Serializable
    An implementation of the Hu–Tucker optimal lexicographical prefix-free code.

    The familiar Huffman coding technique can be extended so to preserve the order in which symbols are given to the coder, in the sense that if j<k, then the j-th symbol will get a code lexicographically smaller than the one assigned to the k-th symbol. This result can be obtained with a small loss in code length (for more details, see the third volume of The Art of Computer Programming).

    A Hu–Tucker coder is built given an array of frequencies corresponding to each symbol. Frequency 0 symbols are allowed, but they will degrade the resulting code.

    The implementation of this class is rather inefficient, and the time required to build a Hu–Tucker code is quadratic in the number of symbols. An O(n log n) implementation is possible, but it requires very sophisticated data structures.

    See Also:
    Serialized Form

    • Field Detail

      • size

        public final int size
        The number of symbols of this coder.

    • Constructor Detail

      • HuTuckerCodec

        public HuTuckerCodec​(int[] frequency)

      • HuTuckerCodec

        public HuTuckerCodec​(long[] frequency)

    • Method Detail

      • coder

        public CodeWordCoder coder()
        Description copied from interface: Codec
        Returns a coder for the compression technique represented by this coded.
        Specified by:
        coder in interface Codec
        Specified by:
        coder in interface PrefixCodec
        Returns:
        a coder for the compression technique represented by this codec.

      • decoder

        public Decoder decoder()
        Description copied from interface: Codec
        Returns a decoder for the compression technique represented by this coded.
        Specified by:
        decoder in interface Codec
        Returns:
        a decoder for the compression technique represented by this codec.

      • size

        public int size()
        Description copied from interface: Codec
        Returns the number of symbols handled by this codec.
        Specified by:
        size in interface Codec
        Returns:
        the number of symbols handled by this codec.

      • codeWords

        public BitVector[] codeWords()
        Description copied from interface: PrefixCodec
        Returns the vector of prefix-free codewords used by this prefix coder.
        Specified by:
        codeWords in interface PrefixCodec
        Returns:
        the vector of prefix-free codewords used by this prefix coder.