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Brace Expansion II

Under the grammar given below, strings can represent a set of lowercase words.

Under the grammar given below, strings can represent a set of lowercase words. Let R(expr) denote the set of words the expression represents.

The grammar can best be understood through simple examples:

Formally, the three rules for our grammar:

Given an expression representing a set of words under the given grammar, return the sorted list of words that the expression represents.

Brace Expansion II diagram

Example 1

Input: expression = "{a,b}{c,{d,e}}"

Output: ["ac","ad","ae","bc","bd","be"]

Example 2

Input: expression = "{{a,z},a{b,c},{ab,z}}"

Output: ["a","ab","ac","z"]

Explanation: Each distinct word is written only once in the final answer.

Constraints

  • 1 <= expression.length <= 60
  • expression[i] consists of '{', '}', ','or lowercase English letters.
  • The given expression represents a set of words based on the grammar given in the description.

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