设集合S由若干单词（英文）组成，给定字符串K，在S中查找与K最佳匹配的结果。最佳匹配的结果定义为：与K有最长共同前缀的字符串。

例：S={abc, bdef, zhen, zhao, abdd}，K1=zhao，K2=abdf，K3=cheng，则与K1最匹配的结果是zhao，与K2最匹配的结果是abdd，与K3最匹配的结果是ε（空串）。

-Set the set S consists of several words (in English), with the given string K, and K to find the best match results in S. The results define the best match for: longest string and K have a common prefix. Example: S = {abc, bdef, zhen, zhao, abdd}, K1 = zhao, K2 = abdf, K3 = cheng, K1 is the best match and the result is zhao, and K2 is the best match abdd, and K3 most result of the matching is ε (the empty string).