code: public static int additiveHash(String key, int prime) {
  		int hash, i;
  		for (hash = key.length(), i = 0; i < key.length(); i++) {
  			hash += key.charAt(i);
  		}
  		return hash % prime;
  	}
docs: 加法hash
  
  @param key 字符串
  @param prime 一个质数
  @return hash结果