Add: Brace Expansion

Author: openset

problems/brace-expansion/README.md

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+<!--|This file generated by command(leetcode description); DO NOT EDIT.    |-->
+<!--+----------------------------------------------------------------------+-->
+<!--|@author    Openset <openset.wang@gmail.com>                           |-->
+<!--|@link      https://github.com/openset                                 |-->
+<!--|@home      https://github.com/openset/leetcode                        |-->
+<!--+----------------------------------------------------------------------+-->
+
+[< Previous](https://github.com/openset/leetcode/tree/master/problems/high-five "High Five")
+　　　　　　　　　　　　　　　　
+[Next >](https://github.com/openset/leetcode/tree/master/problems/confusing-number-ii "Confusing Number II")
+
+## 1087. Brace Expansion (Medium)
+
+
+
+### Related Topics
+  [[Backtracking](https://github.com/openset/leetcode/tree/master/tag/backtracking/README.md)]
+
+### Similar Questions
+  1. [Decode String](https://github.com/openset/leetcode/tree/master/problems/decode-string) (Medium)
+  1. [Letter Case Permutation](https://github.com/openset/leetcode/tree/master/problems/letter-case-permutation) (Easy)
+
+### Hints
+<details>
+<summary>Hint 1</summary>
+All generated strings are of the same size. How can we generate all of these strings?
+</details>
+
+<details>
+<summary>Hint 2</summary>
+Do a backtracking on which each level of it has to choose one single (e.g. 'a') character or any character of the given parenthesized group (e.g. "{a,b,c}")
+</details>