JavaScript:实现按字典顺序查找给定字符串的所有不同的非空子序列算法
/*
* Problem Statement: Find all distinct, non-empty subsequence of given string in lexicographical order using recursive approach.
*
* What is subsequence?
* A Subsequence is sequence obtained by deleting some or no elements without changing the order of elements
* Example: Given a string = "abcd"
* 1. "abc" is a subsequence
* 2. "abd" is a subsequence
* 3. But "ba" is not a subsequence (because order is changed)
*
* What is lexicographical order?
* In simple terms, lexicographical order is dictionary order.
* Example: Given a string = "abcd"
* 1. "abc" will come before "abcd".
* 2. "abd" will come before "ac