趣味算法：返回完全幂的绝对差

之前写过一篇趣味算法，返回不重复数，引得园子里很多算法高手技痒，我看到的关于返回不重复数的文章有好几篇。这使我更坚信，园子是个很好的技术交流平台。前两天又写了一道算法，原题是英文的，本人英文不是太好，初步翻译了一下，效果自认为还过得去，但怕翻译出来误导了大家，特请坤坤和他那边的英语牛人帮忙翻译，在此，我要特别感谢他们。好了，废话少说，上题目：

原：

A number is called a perfect power if it can be written in the form m^k, where m and k are positive integers, and k > 1. Given two positive integers A and B, find the two perfect powers between A and B, inclusive, that are closest to each other, and return the absolute difference between them. If less than two perfect powers exist in the interval, return -1 instead.

译：