/usr/include/fastjet/ is in libfastjet-dev 3.0.6+dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/fastjet/ActiveAreaSpec.hh
/usr/include/fastjet/AreaDefinition.hh
/usr/include/fastjet/CircularRange.hh
/usr/include/fastjet/ClusterSequence.hh
/usr/include/fastjet/ClusterSequence1GhostPassiveArea.hh
/usr/include/fastjet/ClusterSequenceActiveArea.hh
/usr/include/fastjet/ClusterSequenceActiveAreaExplicitGhosts.hh
/usr/include/fastjet/ClusterSequenceArea.hh
/usr/include/fastjet/ClusterSequenceAreaBase.hh
/usr/include/fastjet/ClusterSequencePassiveArea.hh
/usr/include/fastjet/ClusterSequenceStructure.hh
/usr/include/fastjet/ClusterSequenceVoronoiArea.hh
/usr/include/fastjet/ClusterSequenceWithArea.hh
/usr/include/fastjet/CompositeJetStructure.hh
/usr/include/fastjet/Error.hh
/usr/include/fastjet/FunctionOfPseudoJet.hh
/usr/include/fastjet/GhostedAreaSpec.hh
/usr/include/fastjet/JetDefinition.hh
/usr/include/fastjet/LimitedWarning.hh
/usr/include/fastjet/NNH.hh
/usr/include/fastjet/PseudoJet.hh
/usr/include/fastjet/PseudoJetStructureBase.hh
/usr/include/fastjet/RangeDefinition.hh
/usr/include/fastjet/Selector.hh
/usr/include/fastjet/SharedPtr.hh
/usr/include/fastjet/WrappedStructure.hh
/usr/include/fastjet/config.h
/usr/include/fastjet/config_auto.h
/usr/include/fastjet/internal/
/usr/include/fastjet/internal/BasicRandom.hh
/usr/include/fastjet/internal/ClosestPair2D.hh
/usr/include/fastjet/internal/ClosestPair2DBase.hh
/usr/include/fastjet/internal/Dnn2piCylinder.hh
/usr/include/fastjet/internal/Dnn3piCylinder.hh
/usr/include/fastjet/internal/Dnn4piCylinder.hh
/usr/include/fastjet/internal/DnnPlane.hh
/usr/include/fastjet/internal/DynamicNearestNeighbours.hh
/usr/include/fastjet/internal/IsBase.hh
/usr/include/fastjet/internal/LimitedWarning.hh
/usr/include/fastjet/internal/MinHeap.hh
/usr/include/fastjet/internal/SearchTree.hh
/usr/include/fastjet/internal/Triangulation.hh
/usr/include/fastjet/internal/Voronoi.hh
/usr/include/fastjet/internal/base.hh
/usr/include/fastjet/internal/numconsts.hh
/usr/include/fastjet/version.hh