Spec Levels

Levels is a RankDictionary consisting of up to three levels.

/*!
 * @class Levels
 * 
 * @extends RankDictionary
 * 
 * @headerfile <seqan/index.h>
 * 
 * @brief Levels is a @link RankDictionary @endlink consisting of up to three
 *        levels.
 * 
 * @signature template <typename TValue, typename TSpec, typename TConfig>
 *            struct RankDictionary<TValue, Levels<TSpec> >;
 * 
 * @tparam TValue The alphabet type of the wavelet tree.
 * @tparam TSpec A tag for specialization purposes. Default: <tt>void</tt>
 * 
 * This @link RankDictionary @endlink consists of up to three levels of rank
 * infromation, in which one stores information of blocks (1st level) and the
 * other information until a specified block. Combining those two information
 * leads to constant rank dictionary look ups. To reduce space one can increase
 * the number of levels up to three.
 */