参考:
史上最强算法论战：请不要嘻哈，这是哈希
http://chuansong.me/n/1483028
minimal perfect hash function
https://en.wikipedia.org/wiki/Perfect_hash_function
http://mp.weixin.qq.com/s?__biz=MjM5MTQzNzU2NA==&mid=207841440&idx=1&sn=e7c993bfdd5d39de9c24a6730f78ce5e&scene=1&from=singlemessage&isappinstalled=0#rd
