Package it.unimi.dsi.sux4j.bits

Interface Select

All Superinterfaces:
Serializable
All Known Implementing Classes:
HintedBsearchSelect, RankSelect, Select9, SimpleBigSelect, SimpleSelect, SparseSelect
public interface Select extends Serializable
A data structure providing selection over a bit array.

Selection is a basic building blocks for most succinct data structures. Usually, instances of this class class provide quick (e.g., constant-time) selection.

This interface specifies a zero-based selection. More precisely, select is applied to a bit vector in which bits positions are numbered starting from zero. Then, select(r) is the position of the leftmost bit set to one and preceded by r ones. There are also default bulk methods select(long, long[], int, int) and select(long) whose implementation delegates to select(long) but might be implemented more efficiently.

A number of equations link rank() and select():

  • rank(0)=0;
  • rank(length()) is the number of ones in the bit vector;
  • if r < rank(length()), then rank(select(r))==r;
  • if p ≤ length(), then p≤select(rank(p)), and equality holds iff there is a one at position p.
See Also:
API Notes:
From Sux4J 5.2.0, the select(long) method is no longer required to return −1 when no bit with the given rank exists. If you relied on such behavior, please test the argument before calling select(long). Implementations might provide assertions to check the argument for correctness.

  • Method Summary

    Modifier and Type
    Method
    Description
    BitVector
    bitVector()
    Returns the bit vector indexed by this structure.
    long
    numBits()
    Returns the overall number of bits allocated by this structure.
    long
    select(long rank)
    Returns the position of the bit of given rank.
    default long[]
    select(long rank, long[] dest)
    Performs a bulk select of consecutive ranks into a given array.
    default long[]
    select(long rank, long[] dest, int offset, int length)
    Performs a bulk select of consecutive ranks into a given array fragment.

  • Method Details

    • select

      long select(long rank)
      Returns the position of the bit of given rank. Equivalently, returns the greatest position that is preceded by the specified number of ones.
      Parameters:
      rank - a rank.
      Returns:
      the position of the bit of given rank; if no such bit exists, behavior is undefined .
      API Notes:
      From Sux4J 5.2.0, this method is no longer required to return −1 when no bit with the given rank exists. If you relied on such behavior, please test the argument before calling this method. Implementations might provide assertions to check the argument for correctness.

    • select

      default long[] select(long rank, long[] dest, int offset, int length)
      Performs a bulk select of consecutive ranks into a given array fragment.
      Parameters:
      rank - the first rank to select.
      dest - the destination array; it will be filled with length positions of consecutive bits starting at position offset; must be of length greater than offset.
      offset - the first bit position written in dest.
      length - the number of bit positions in dest starting at offset.
      Returns:
      dest
      See Also:
      API Notes:
      Implementations are allowed to require that dest be of length greater than offset even if length is zero.
      Implementation Specification:
      This implementation just makes multiple calls to select(long).

    • select

      default long[] select(long rank, long[] dest)
      Performs a bulk select of consecutive ranks into a given array.
      Parameters:
      rank - the first rank to select.
      dest - the destination array; it will be filled with position of consecutive bits.
      Returns:
      dest
      See Also:
      API Notes:
      Implementations are allowed to require that dest be of length greater than zero.
      Implementation Specification:
      This implementation just delegates to select(long, long[], int, int).

    • bitVector

      BitVector bitVector()
      Returns the bit vector indexed by this structure.

      Note that you are not supposed to modify the returned vector.

      Returns:
      the bit vector indexed by this structure.

    • numBits

      long numBits()
      Returns the overall number of bits allocated by this structure.
      Returns:
      the overall number of bits allocated by this structure (not including the bits of the indexed vector).