Package it.unimi.dsi.sux4j.bits
Interface Select
 All Superinterfaces:
java.io.Serializable
 All Known Implementing Classes:
HintedBsearchSelect
,RankSelect
,Select9
,SimpleSelect
,SparseSelect
public interface Select
extends java.io.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.
There is some variance in the literature about the exact semantics of selection—in most cases, it is a matter of offbyones. This interface specifies a zerobased 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.
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())
, thenrank(select(r))==r
;  if
r ≥ rank(length())
, thenselect(r)=1
;  if
p ≤ length()
, thenp≤select(rank(p))
, and equality holds iff there is a one at positionp
.

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 position exists, −1 is returned.

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).
