# MPI-I-95-1-022

## New deterministic algorithms for counting pairs of intersecting segments and off-line triangle range searching

### Pellegrini, M.

#### July 1995, 12 pages.

.

##### Status: available - back from printing

We describe a new method for decomposing planar sets of segments and
points.
Using this method we obtain
new efficient {\em deterministic}
algorithms for counting pairs of intersecting
segments, and for answering off-line triangle range queries.
In particular we obtain the following results:
\noindent
(1)
Given $n$ segments in the plane, the number $K$ of
pairs of intersecting segments is computed in time
$O(n^{1+\epsilon} + K^{1/3}n^{2/3 + \epsilon})$, where
$\epsilon >0$ an arbitrarily small constant.
\noindent
(2)
Given $n$ segments in the plane which are coloured with two colours,
the number of pairs of {\em bi-chromatic} intersecting segments is
computed in time
$O(n^{1+\epsilon} + K_m^{1/3}n^{2/3 +\epsilon})$, where $K_m$ is the number of {\em
mono-chromatic} intersections, and $\epsilon >0$ is an arbitrarily small constant.
\noindent
(3)
Given $n$ weighted points and $n$ triangles on a plane,
the sum of weights of points in each triangle is computed
in time $O(n^{1+\epsilon} + {\cal K}^{1/3}n^{2/3 +\epsilon})$,
where ${\cal K}$ is the number of vertices in the arrangement of the triangles,
and $\epsilon>0$ an arbitrarily small constant. The above bounds depend sub-linearly on the number of
intersections among segments $K$ (resp. $K_m$, ${\cal K}$), which is
desirable since $K$ (resp. $K_m$, ${\cal K}$)
can range from zero to $O(n^2)$. All of the
above algorithms use optimal $\Theta(n)$ storage. The constants of
proportionality in the big-Oh notation increase as $\epsilon$ decreases.
These results are
based on properties of the sparse nets introduced by Chazelle.

**URL to this document: **https://domino.mpi-inf.mpg.de/internet/reports.nsf/NumberView/1995-1-022

**BibTeX**
`@TECHREPORT{``Pellegrini95``,`

` AUTHOR = {Pellegrini, M.},`

` TITLE = {New deterministic algorithms for counting pairs of intersecting segments and off-line triangle range searching},`

` TYPE = {Research Report},`

` INSTITUTION = {Max-Planck-Institut f{\"u}r Informatik},`

` ADDRESS = {Im Stadtwald, D-66123 Saarbr{\"u}cken, Germany},`

` NUMBER = {MPI-I-95-1-022},`

` MONTH = {July},`

` YEAR = {1995},`

` ISSN = {0946-011X},`

`}`