Procedure: the proposed VNS algorithm
Initialization: Define the set of neighborhood structures 𝑁 𝑆 𝑆 𝑘 , for 𝑘 = 1 ,…, 𝑘 m a x ;
      find a initial solution 𝑥 by SRF heuristic;
      choose a stopping criterion.
𝑘 = 1
while the stopping criterion is not met do
 perform the neighborhood search structure 𝑁 𝑆 𝑆 𝑘
if  x is improved do
  continue the search with 𝑁 𝑆 𝑆 𝑘
  k = k mod 𝑘 m a x + 1
end  if
end  while
Algorithm 5: Procedure of the proposed VNS algorithm.