在数据加密和数据压缩中常需要对特殊的字符串进行编码。给定的字母表 A 由 26 个 写英文字母组成 A={a,b,…,z}。该字母表产生的升序字符串是指字符串中字母按照从左到 右出现的次序与字母在字母表中出现的次序相同,且每个字符最多出现 1 次。例如,a,b,ab, bc,xyz 等字符串都是升序字符串。-In the data encryption and data compression is often the need for special strings to be encoded. A given alphabet letters of the alphabet by 26 Composition A = {a, b, ..., z}. The resulting string in ascending alphabet letters refer to the same string that appears in the order　left to right order with the letters appear in the alphabet, and each character appears at most a times. For example, a, b, ab, bc, xyz ascending like strings are strings.