  We present a novel method for efficient direct integration of gravitational
N-body systems with a large variation in characteristic time scales. The method
is based on a recursive and adaptive partitioning of the system based on the
connected components of the graph generated by the particle distribution
combined with an interaction-specific time step criterion. It uses an explicit
and approximately time-symmetric time step criterion, and conserves linear and
angular momentum to machine precision. In numerical tests on astrophysically
relevant setups, the method compares favourably to both alternative
Hamiltonian-splitting integrators as well as recently developed block time
step-based GPU-accelerated Hermite codes. Our reference implementation is
incorporated in the HUAYNO code, which is freely available as a part of the
AMUSE framework.
