Abstract
Stick graphs are intersection graphs of horizontal
and vertical line seg- ments that all touch a line
of slope −1 and lie above this line. De Luca et
al. GD'18 considered the recognition problem of
stick graphs when no order is given (STICK), when
the order of either one of the two sets is given
(STICK$_A$), and when the order of both sets is
given (STICK$_AB$). They showed how to solve
STICK$_AB$ efficiently. In this paper, we
improve the running time of their algorithm, and we
solve STICK$_A$ efficiently. Further, we consider
variants of these problems where the lengths of the
sticks are given as input. We show that these
variants of STICK, STICK$_A$, and STICK$_AB$ are
all NP-complete. On the positive side, we give an
efficient solution for STICK$_AB$ with fixed stick
lengths if there are no isolated vertices.
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