1087. Brace Expansion

https://leetcode.com/problems/brace-expansion

Description

You are given a string s representing a list of words. Each letter in the word has one or more options.

• If there is one option, the letter is represented as is.

• If there is more than one option, then curly braces delimit the options. For example, "{a,b,c}" represents options ["a", "b", "c"].

For example, if s = "a{b,c}", the first character is always 'a', but the second character can be 'b' or 'c'. The original list is ["ab", "ac"].

Return all words that can be formed in this manner, sorted in lexicographical order.

Example 1:

**Input:** s = "{a,b}c{d,e}f"
**Output:** ["acdf","acef","bcdf","bcef"]

Example 2:

**Input:** s = "abcd"
**Output:** ["abcd"]

Constraints:

• 1 <= s.length <= 50

• s consists of curly brackets '{}', commas ',', and lowercase English letters.

• s is guaranteed to be a valid input.

• There are no nested curly brackets.

• All characters inside a pair of consecutive opening and ending curly brackets are different.

ac