编程列出一个字符串的全字符组合情况，原始字符串中没有重复字符，例如：
*原始字符串是"abc"，打印得到下列所有组合情况：
*"a" "b" "c"
*"ab" "bc" "ca" "ba" "cb" "ac"
*"abc" "acb" "bac" "bca" "cab" "cba"

编程列出一个字符串的全字符组合情况，原始字符串中没有重复字符，例如：
*原始字符串是"abc"，打印得到下列所有组合情况：
*"a" "b" "c"
*"ab" "bc" "ca" "ba" "cb" "ac"
*"abc" "acb" "bac" "bca" "cab" "cba"