Brace Expansion II
<p>Under the grammar given below, strings can represent a set of lowercase words. Let&nbsp;<code>R(expr)</code>&nbsp;denote the set of words the expression represents.</p>

<p>The grammar can best be understood through simple examples:</p>

<ul>
	<li>Single letters represent a singleton set containing that word.
	<ul>
		<li><code>R(&quot;a&quot;) = {&quot;a&quot;}</code></li>
		<li><code>R(&quot;w&quot;) = {&quot;w&quot;}</code></li>
	</ul>
	</li>
	<li>When we take a comma-delimited list of two or more expressions, we take the union of possibilities.
	<ul>
		<li><code>R(&quot;{a,b,c}&quot;) = {&quot;a&quot;,&quot;b&quot;,&quot;c&quot;}</code></li>
		<li><code>R(&quot;{{a,b},{b,c}}&quot;) = {&quot;a&quot;,&quot;b&quot;,&quot;c&quot;}</code> (notice the final set only contains each word at most once)</li>
	</ul>
	</li>
	<li>When we concatenate two expressions, we take the set of possible concatenations between two words where the first word comes from the first expression and the second word comes from the second expression.
	<ul>
		<li><code>R(&quot;{a,b}{c,d}&quot;) = {&quot;ac&quot;,&quot;ad&quot;,&quot;bc&quot;,&quot;bd&quot;}</code></li>
		<li><code>R(&quot;a{b,c}{d,e}f{g,h}&quot;) = {&quot;abdfg&quot;, &quot;abdfh&quot;, &quot;abefg&quot;, &quot;abefh&quot;, &quot;acdfg&quot;, &quot;acdfh&quot;, &quot;acefg&quot;, &quot;acefh&quot;}</code></li>
	</ul>
	</li>
</ul>

<p>Formally, the three rules for our grammar:</p>

<ul>
	<li>For every lowercase letter <code>x</code>, we have <code>R(x) = {x}</code>.</li>
	<li>For expressions <code>e<sub>1</sub>, e<sub>2</sub>, ... , e<sub>k</sub></code> with <code>k &gt;= 2</code>, we have <code>R({e<sub>1</sub>, e<sub>2</sub>, ...}) = R(e<sub>1</sub>) &cup; R(e<sub>2</sub>) &cup; ...</code></li>
	<li>For expressions <code>e<sub>1</sub></code> and <code>e<sub>2</sub></code>, we have <code>R(e<sub>1</sub> + e<sub>2</sub>) = {a + b for (a, b) in R(e<sub>1</sub>) &times; R(e<sub>2</sub>)}</code>, where <code>+</code> denotes concatenation, and <code>&times;</code> denotes the cartesian product.</li>
</ul>

<p>Given an expression representing a set of words under the given grammar, return <em>the sorted list of words that the expression represents</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> expression = &quot;{a,b}{c,{d,e}}&quot;
<strong>Output:</strong> [&quot;ac&quot;,&quot;ad&quot;,&quot;ae&quot;,&quot;bc&quot;,&quot;bd&quot;,&quot;be&quot;]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> expression = &quot;{{a,z},a{b,c},{ab,z}}&quot;
<strong>Output:</strong> [&quot;a&quot;,&quot;ab&quot;,&quot;ac&quot;,&quot;z&quot;]
<strong>Explanation:</strong> Each distinct word is written only once in the final answer.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= expression.length &lt;= 60</code></li>
	<li><code>expression[i]</code> consists of <code>&#39;{&#39;</code>, <code>&#39;}&#39;</code>, <code>&#39;,&#39;</code>or lowercase English letters.</li>
	<li>The given&nbsp;<code>expression</code>&nbsp;represents a set of words based on the grammar given in the description.</li>
</ul>

['brace-expansion']
[]
[{"value": "cpp", "text": "C++", "defaultCode": "class Solution {\npublic:\n    vector<string> braceExpansionII(string expression) {\n        \n    }\n};"}, {"value": "java", "text": "Java", "defaultCode": "class Solution {\n    public List<String> braceExpansionII(String expression) {\n        \n    }\n}"}, {"value": "python", "text": "Python", "defaultCode": "class Solution(object):\n    def braceExpansionII(self, expression):\n        \"\"\"\n        :type expression: str\n        :rtype: List[str]\n        \"\"\"\n        "}, {"value": "python3", "text": "Python3", "defaultCode": "class Solution:\n    def braceExpansionII(self, expression: str) -> List[str]:\n        "}, {"value": "c", "text": "C", "defaultCode": "/**\n * Note: The returned array must be malloced, assume caller calls free().\n */\nchar** braceExpansionII(char* expression, int* returnSize) {\n    \n}"}, {"value": "csharp", "text": "C#", "defaultCode": "public class Solution {\n    public IList<string> BraceExpansionII(string expression) {\n        \n    }\n}"}, {"value": "javascript", "text": "JavaScript", "defaultCode": "/**\n * @param {string} expression\n * @return {string[]}\n */\nvar braceExpansionII = function(expression) {\n    \n};"}, {"value": "typescript", "text": "TypeScript", "defaultCode": "function braceExpansionII(expression: string): string[] {\n    \n};"}, {"value": "php", "text": "PHP", "defaultCode": "class Solution {\n\n    /**\n     * @param String $expression\n     * @return String[]\n     */\n    function braceExpansionII($expression) {\n        \n    }\n}"}, {"value": "swift", "text": "Swift", "defaultCode": "class Solution {\n    func braceExpansionII(_ expression: String) -> [String] {\n        \n    }\n}"}, {"value": "kotlin", "text": "Kotlin", "defaultCode": "class Solution {\n    fun braceExpansionII(expression: String): List<String> {\n        \n    }\n}"}, {"value": "dart", "text": "Dart", "defaultCode": "class Solution {\n  List<String> braceExpansionII(String expression) {\n    \n  }\n}"}, {"value": "golang", "text": "Go", "defaultCode": "func braceExpansionII(expression string) []string {\n    \n}"}, {"value": "ruby", "text": "Ruby", "defaultCode": "# @param {String} expression\n# @return {String[]}\ndef brace_expansion_ii(expression)\n    \nend"}, {"value": "scala", "text": "Scala", "defaultCode": "object Solution {\n    def braceExpansionII(expression: String): List[String] = {\n        \n    }\n}"}, {"value": "rust", "text": "Rust", "defaultCode": "impl Solution {\n    pub fn brace_expansion_ii(expression: String) -> Vec<String> {\n        \n    }\n}"}, {"value": "racket", "text": "Racket", "defaultCode": "(define/contract (brace-expansion-ii expression)\n  (-> string? (listof string?))\n  )"}, {"value": "erlang", "text": "Erlang", "defaultCode": "-spec brace_expansion_ii(Expression :: unicode:unicode_binary()) -> [unicode:unicode_binary()].\nbrace_expansion_ii(Expression) ->\n  ."}, {"value": "elixir", "text": "Elixir", "defaultCode": "defmodule Solution do\n  @spec brace_expansion_ii(expression :: String.t) :: [String.t]\n  def brace_expansion_ii(expression) do\n    \n  end\nend"}]
{
  "name": "braceExpansionII",
  "params": [
    {
      "name": "expression",
      "type": "string"
    }
  ],
  "return": {
    "type": "list<string>"
  }
}

{"cpp": ["C++", "<p>Compiled with <code> clang 19 </code> using the latest C++ 23 standard, and <code>libstdc++</code> provided by GCC 14.</p>\r\n\r\n<p>Your code is compiled with level two optimization (<code>-O2</code>). <a href=\"https://github.com/google/sanitizers/wiki/AddressSanitizer\" target=\"_blank\">AddressSanitizer</a> is also enabled to help detect out-of-bounds and use-after-free bugs.</p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>"], "java": ["Java", "<p><code>OpenJDK 21</code>. Using compile arguments: <code>--enable-preview --release 21</code></p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>\r\n<p>Includes <code>Pair</code> class from https://docs.oracle.com/javase/8/javafx/api/javafx/util/Pair.html.</p>"], "python": ["Python", "<p><code>Python 2.7.18</code>.</p>\r\n\r\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\"https://docs.python.org/2/library/array.html\" target=\"_blank\">array</a>, <a href=\"https://docs.python.org/2/library/bisect.html\" target=\"_blank\">bisect</a>, <a href=\"https://docs.python.org/2/library/collections.html\" target=\"_blank\">collections</a>. If you need more libraries, you can import it yourself.</p>\r\n\r\n<p>For Map/TreeMap data structure, you may use <a href=\"http://www.grantjenks.com/docs/sortedcontainers/\" target=\"_blank\">sortedcontainers</a> library.</p>\r\n\r\n<p>Note that Python 2.7 <a href=\"https://www.python.org/dev/peps/pep-0373/\" target=\"_blank\">is not maintained anymore</a>. For the latest Python, please choose Python3 instead.</p>"], "c": ["C", "<p>Compiled with <code>gcc 14</code> using the gnu11 standard.</p>\r\n\r\n<p>Your code is compiled with level one optimization (<code>-O2</code>). <a href=\"https://github.com/google/sanitizers/wiki/AddressSanitizer\" target=\"_blank\">AddressSanitizer</a> is also enabled to help detect out-of-bounds and use-after-free bugs.</p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>\r\n\r\n<p>For hash table operations, you may use <a href=\"https://troydhanson.github.io/uthash/\" target=\"_blank\">uthash</a>. \"uthash.h\" is included by default. Below are some examples:</p>\r\n\r\n<p><b>1. Adding an item to a hash.</b>\r\n<pre>\r\nstruct hash_entry {\r\n    int id;            /* we'll use this field as the key */\r\n    char name[10];\r\n    UT_hash_handle hh; /* makes this structure hashable */\r\n};\r\n\r\nstruct hash_entry *users = NULL;\r\n\r\nvoid add_user(struct hash_entry *s) {\r\n    HASH_ADD_INT(users, id, s);\r\n}\r\n</pre>\r\n</p>\r\n\r\n<p><b>2. Looking up an item in a hash:</b>\r\n<pre>\r\nstruct hash_entry *find_user(int user_id) {\r\n    struct hash_entry *s;\r\n    HASH_FIND_INT(users, &user_id, s);\r\n    return s;\r\n}\r\n</pre>\r\n</p>\r\n\r\n<p><b>3. Deleting an item in a hash:</b>\r\n<pre>\r\nvoid delete_user(struct hash_entry *user) {\r\n    HASH_DEL(users, user);  \r\n}\r\n</pre>\r\n</p>"], "csharp": ["C#", "<p><a href=\"https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13\" target=\"_blank\">C# 13</a> with .NET 9 runtime</p>"], "javascript": ["JavaScript", "<p><code>Node.js 22.14.0</code>.</p>\r\n\r\n<p>Your code is run with <code>--harmony</code> flag, enabling <a href=\"http://node.green/\" target=\"_blank\">new ES6 features</a>.</p>\r\n\r\n<p><a href=\"https://lodash.com\" target=\"_blank\">lodash.js</a> library is included by default.</p>\r\n\r\n<p>For Priority Queue / Queue data structures, you may use 6.3.2 version of <a href=\"https://github.com/datastructures-js/priority-queue/tree/v6.3.2\" target=\"_blank\">datastructures-js/priority-queue</a> and 4.2.3 version of <a href=\"https://github.com/datastructures-js/queue/tree/v4.2.3\" target=\"_blank\">datastructures-js/queue</a> and 1.0.4 version of <a href=\"https://github.com/datastructures-js/deque/tree/v1.0.4\" target=\"_blank\">datastructures-js/deque</a>.</p>"], "ruby": ["Ruby", "<p><code>Ruby 3.2</code></p>\r\n\r\n<p>Some common data structure implementations are provided in the Algorithms module: https://www.rubydoc.info/github/kanwei/algorithms/Algorithms</p>"], "swift": ["Swift", "<p><code>Swift 6.0</code>.</p>\r\n\r\n<p>You may use the following packages:<br/>\r\n<a href=\"https://github.com/apple/swift-algorithms/tree/1.2.0\" target=\"_blank\">swift-algorithms 1.2.0</a><br/>\r\n<a href=\"https://github.com/apple/swift-collections/tree/1.1.4\" target=\"_blank\">swift-collections 1.1.4</a><br/>\r\n<a href=\"https://github.com/apple/swift-numerics/tree/1.0.2\" target=\"_blank\">swift-numerics 1.0.2</a></p>"], "golang": ["Go", "<p><code>Go 1.23</code></p>\r\n<p>Support <a href=\"https://pkg.go.dev/github.com/emirpasic/gods@v1.18.1\" target=\"_blank\">https://pkg.go.dev/github.com/emirpasic/gods@v1.18.1</a> and <a href=\"https://pkg.go.dev/github.com/emirpasic/gods/v2@v2.0.0-alpha\" target=\"_blank\">https://pkg.go.dev/github.com/emirpasic/gods/v2@v2.0.0-alpha</a> library.</p>"], "python3": ["Python3", "<p><code>Python 3.11</code>.</p>\r\n\r\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\"https://docs.python.org/3/library/array.html\" target=\"_blank\">array</a>, <a href=\"https://docs.python.org/3/library/bisect.html\" target=\"_blank\">bisect</a>, <a href=\"https://docs.python.org/3/library/collections.html\" target=\"_blank\">collections</a>. If you need more libraries, you can import it yourself.</p>\r\n\r\n<p>For Map/TreeMap data structure, you may use <a href=\"http://www.grantjenks.com/docs/sortedcontainers/\" target=\"_blank\">sortedcontainers</a> library.</p>"], "scala": ["Scala", "<p><code>Scala 3.3.1</code>.</p>"], "kotlin": ["Kotlin", "<p><code>Kotlin 2.1.10</code>.</p>"], "rust": ["Rust", "<p><code>Rust 1.85.0</code>. Your code will be compiled with <code>opt-level</code> 2.</p>\r\n\r\n<p>Supports <a href=\"https://crates.io/crates/rand\" target=\"_blank\">rand v0.8</a> and <a href=\"https://crates.io/crates/regex\" target=\"_blank\">regex\u00a0v1</a> and <a href=\"https://crates.io/crates/itertools\" target=\"_blank\">itertools\u00a0v0.14</a> from crates.io</p>"], "php": ["PHP", "<p><code>PHP 8.2</code>.</p>\r\n<p>With bcmath module</p>"], "typescript": ["Typescript", "<p><code>TypeScript 5.7.3, Node.js 22.14.0</code>.</p>\r\n\r\n<p>Compile Options: <code>--alwaysStrict --strictBindCallApply --strictFunctionTypes --target ES2024</code></p>\r\n\r\n<p><a href=\"https://lodash.com\" target=\"_blank\">lodash.js</a> library is included by default.</p>\r\n\r\n<p>For Priority Queue / Queue data structures, you may use 6.3.2 version of <a href=\"https://github.com/datastructures-js/priority-queue/tree/v6.3.2\" target=\"_blank\">datastructures-js/priority-queue</a> and 4.2.3 version of <a href=\"https://github.com/datastructures-js/queue/tree/v4.2.3\" target=\"_blank\">datastructures-js/queue</a> and 1.0.4 version of <a href=\"https://github.com/datastructures-js/deque/tree/v1.0.4\" target=\"_blank\">datastructures-js/deque</a>.</p>"], "racket": ["Racket", "<p><a href=\"https://docs.racket-lang.org/guide/performance.html#%28tech._c%29\" target=\"_blank\">Racket CS</a> v8.15</p>\r\n\r\n<p>Using <code>#lang racket</code></p>\r\n\r\n<p>Required <code>data/gvector data/queue data/order data/heap</code> automatically for your convenience</p>"], "erlang": ["Erlang", "Erlang/OTP 26"], "elixir": ["Elixir", "Elixir 1.17 with Erlang/OTP 26"], "dart": ["Dart", "<p>Dart 3.2. You may use package <a href=\"https://pub.dev/packages/collection/versions/1.18.0\" target=\"_blank\">collection</a></p>\r\n\r\n<p>Your code will be run directly without compiling</p>"]}
['String', 'Backtracking', 'Stack', 'Breadth-First Search']