code: def strategyKLogN(kls, n, k=4):
  		
  		assert(k>1)
  		s = set([n])
  		i = 0
  		
  		while k**i <= n:
  			s.update(range(n, n-k*k**i, -k**i))
  			i += 1
  			n -= n % k**i
  		
  		return set(map(str, filter(lambda x:x>=0, s)))
docs: Return the directory names to preserve under the KLogN purge strategy.