A third-order subcell finite volume gas-kinetic scheme for the Euler and Navier-Stokes equations on triangular meshes

•A subcell finite volume gas-kinetic scheme is developed on triangular meshes.•A constrained least-square reconstruction is adopted to improve the efficiency.•The inviscid and viscous fluxes are coupled and computed uniformly.•It is third-order accurate in space and time with a single stage and without using quadrature points.•The efficiency is higher than the third-order k-exact gas-kinetic scheme.