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# 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

```java
```