字典序问题。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 个小

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。-The lexicographically problem. Data encryption and data compression is often the need for special string encoded. Given alphabet A is written by 26 small English alphabet A = {a, b, ..., z}. The ascending order of the alphabet produced the string is a string of letters in the same in accordance with the order of appearance of the left to right order of appearance of the letters in the alphabet, and each character up to 1 occurrence.