Then it obtains minimal number of snow sweeprs and limit height of snow after the task has been finished by snow sweeper.

Analysis on the least gears in Gear Mechanism;

Using the coutraction technique,we gencralize some results on Hamiltonian digraphs,and present some sufficient conditions involving minimum semi-degree,minimum degree sum and the number of arcs of arcs to force a digraph to be strongly Hamiltonian-connected.