def shell_sort(a)
  n=a.length
  h=1

  while (h<n/3)  #for computing increment factor "h"
    h= (3*h)+1
  end

  while h>=1
    # Logic of insertion sort with inrement steps of "h"
    for i in h...n
      j=i
      while j>=h
        if a[j-h]>a[j]
          temp=a[j]
          a[j]=a[j-h]
          a[j-h]=temp
        end
        j-=h
      end
    end
    h/=3
  end

  return a

end