Iterator for Combination
<p>Design the <code>CombinationIterator</code> class:</p>

<ul>
	<li><code>CombinationIterator(string characters, int combinationLength)</code> Initializes the object with a string <code>characters</code> of <strong>sorted distinct</strong> lowercase English letters and a number <code>combinationLength</code> as arguments.</li>
	<li><code>next()</code> Returns the next combination of length <code>combinationLength</code> in <strong>lexicographical order</strong>.</li>
	<li><code>hasNext()</code> Returns <code>true</code> if and only if there exists a next combination.</li>
</ul>

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

<pre>
<strong>Input</strong>
[&quot;CombinationIterator&quot;, &quot;next&quot;, &quot;hasNext&quot;, &quot;next&quot;, &quot;hasNext&quot;, &quot;next&quot;, &quot;hasNext&quot;]
[[&quot;abc&quot;, 2], [], [], [], [], [], []]
<strong>Output</strong>
[null, &quot;ab&quot;, true, &quot;ac&quot;, true, &quot;bc&quot;, false]

<strong>Explanation</strong>
CombinationIterator itr = new CombinationIterator(&quot;abc&quot;, 2);
itr.next();    // return &quot;ab&quot;
itr.hasNext(); // return True
itr.next();    // return &quot;ac&quot;
itr.hasNext(); // return True
itr.next();    // return &quot;bc&quot;
itr.hasNext(); // return False
</pre>

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

<ul>
	<li><code>1 &lt;= combinationLength &lt;= characters.length &lt;= 15</code></li>
	<li>All the characters of <code>characters</code> are <strong>unique</strong>.</li>
	<li>At most <code>10<sup>4</sup></code> calls will be made to <code>next</code> and <code>hasNext</code>.</li>
	<li>It is guaranteed that all calls of the function <code>next</code> are valid.</li>
</ul>

[]
[]
[{"value": "cpp", "text": "C++", "defaultCode": "class CombinationIterator {\npublic:\n    CombinationIterator(string characters, int combinationLength) {\n        \n    }\n    \n    string next() {\n        \n    }\n    \n    bool hasNext() {\n        \n    }\n};\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * CombinationIterator* obj = new CombinationIterator(characters, combinationLength);\n * string param_1 = obj->next();\n * bool param_2 = obj->hasNext();\n */"}, {"value": "java", "text": "Java", "defaultCode": "class CombinationIterator {\n\n    public CombinationIterator(String characters, int combinationLength) {\n        \n    }\n    \n    public String next() {\n        \n    }\n    \n    public boolean hasNext() {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * CombinationIterator obj = new CombinationIterator(characters, combinationLength);\n * String param_1 = obj.next();\n * boolean param_2 = obj.hasNext();\n */"}, {"value": "python", "text": "Python", "defaultCode": "class CombinationIterator(object):\n\n    def __init__(self, characters, combinationLength):\n        \"\"\"\n        :type characters: str\n        :type combinationLength: int\n        \"\"\"\n        \n\n    def next(self):\n        \"\"\"\n        :rtype: str\n        \"\"\"\n        \n\n    def hasNext(self):\n        \"\"\"\n        :rtype: bool\n        \"\"\"\n        \n\n\n# Your CombinationIterator object will be instantiated and called as such:\n# obj = CombinationIterator(characters, combinationLength)\n# param_1 = obj.next()\n# param_2 = obj.hasNext()"}, {"value": "python3", "text": "Python3", "defaultCode": "class CombinationIterator:\n\n    def __init__(self, characters: str, combinationLength: int):\n        \n\n    def next(self) -> str:\n        \n\n    def hasNext(self) -> bool:\n        \n\n\n# Your CombinationIterator object will be instantiated and called as such:\n# obj = CombinationIterator(characters, combinationLength)\n# param_1 = obj.next()\n# param_2 = obj.hasNext()"}, {"value": "c", "text": "C", "defaultCode": "\n\n\ntypedef struct {\n    \n} CombinationIterator;\n\n\nCombinationIterator* combinationIteratorCreate(char* characters, int combinationLength) {\n    \n}\n\nchar* combinationIteratorNext(CombinationIterator* obj) {\n    \n}\n\nbool combinationIteratorHasNext(CombinationIterator* obj) {\n    \n}\n\nvoid combinationIteratorFree(CombinationIterator* obj) {\n    \n}\n\n/**\n * Your CombinationIterator struct will be instantiated and called as such:\n * CombinationIterator* obj = combinationIteratorCreate(characters, combinationLength);\n * char* param_1 = combinationIteratorNext(obj);\n \n * bool param_2 = combinationIteratorHasNext(obj);\n \n * combinationIteratorFree(obj);\n*/"}, {"value": "csharp", "text": "C#", "defaultCode": "public class CombinationIterator {\n\n    public CombinationIterator(string characters, int combinationLength) {\n        \n    }\n    \n    public string Next() {\n        \n    }\n    \n    public bool HasNext() {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * CombinationIterator obj = new CombinationIterator(characters, combinationLength);\n * string param_1 = obj.Next();\n * bool param_2 = obj.HasNext();\n */"}, {"value": "javascript", "text": "JavaScript", "defaultCode": "/**\n * @param {string} characters\n * @param {number} combinationLength\n */\nvar CombinationIterator = function(characters, combinationLength) {\n    \n};\n\n/**\n * @return {string}\n */\nCombinationIterator.prototype.next = function() {\n    \n};\n\n/**\n * @return {boolean}\n */\nCombinationIterator.prototype.hasNext = function() {\n    \n};\n\n/** \n * Your CombinationIterator object will be instantiated and called as such:\n * var obj = new CombinationIterator(characters, combinationLength)\n * var param_1 = obj.next()\n * var param_2 = obj.hasNext()\n */"}, {"value": "typescript", "text": "TypeScript", "defaultCode": "class CombinationIterator {\n    constructor(characters: string, combinationLength: number) {\n        \n    }\n\n    next(): string {\n        \n    }\n\n    hasNext(): boolean {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * var obj = new CombinationIterator(characters, combinationLength)\n * var param_1 = obj.next()\n * var param_2 = obj.hasNext()\n */"}, {"value": "php", "text": "PHP", "defaultCode": "class CombinationIterator {\n    /**\n     * @param String $characters\n     * @param Integer $combinationLength\n     */\n    function __construct($characters, $combinationLength) {\n        \n    }\n  \n    /**\n     * @return String\n     */\n    function next() {\n        \n    }\n  \n    /**\n     * @return Boolean\n     */\n    function hasNext() {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * $obj = CombinationIterator($characters, $combinationLength);\n * $ret_1 = $obj->next();\n * $ret_2 = $obj->hasNext();\n */"}, {"value": "swift", "text": "Swift", "defaultCode": "\nclass CombinationIterator {\n\n    init(_ characters: String, _ combinationLength: Int) {\n        \n    }\n    \n    func next() -> String {\n        \n    }\n    \n    func hasNext() -> Bool {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * let obj = CombinationIterator(characters, combinationLength)\n * let ret_1: String = obj.next()\n * let ret_2: Bool = obj.hasNext()\n */"}, {"value": "kotlin", "text": "Kotlin", "defaultCode": "class CombinationIterator(characters: String, combinationLength: Int) {\n\n    fun next(): String {\n        \n    }\n\n    fun hasNext(): Boolean {\n        \n    }\n\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * var obj = CombinationIterator(characters, combinationLength)\n * var param_1 = obj.next()\n * var param_2 = obj.hasNext()\n */"}, {"value": "dart", "text": "Dart", "defaultCode": "class CombinationIterator {\n\n  CombinationIterator(String characters, int combinationLength) {\n    \n  }\n  \n  String next() {\n    \n  }\n  \n  bool hasNext() {\n    \n  }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * CombinationIterator obj = CombinationIterator(characters, combinationLength);\n * String param1 = obj.next();\n * bool param2 = obj.hasNext();\n */"}, {"value": "golang", "text": "Go", "defaultCode": "type CombinationIterator struct {\n    \n}\n\n\nfunc Constructor(characters string, combinationLength int) CombinationIterator {\n    \n}\n\n\nfunc (this *CombinationIterator) Next() string {\n    \n}\n\n\nfunc (this *CombinationIterator) HasNext() bool {\n    \n}\n\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * obj := Constructor(characters, combinationLength);\n * param_1 := obj.Next();\n * param_2 := obj.HasNext();\n */"}, {"value": "ruby", "text": "Ruby", "defaultCode": "class CombinationIterator\n\n=begin\n    :type characters: String\n    :type combination_length: Integer\n=end\n    def initialize(characters, combination_length)\n        \n    end\n\n\n=begin\n    :rtype: String\n=end\n    def next()\n        \n    end\n\n\n=begin\n    :rtype: Boolean\n=end\n    def has_next()\n        \n    end\n\n\nend\n\n# Your CombinationIterator object will be instantiated and called as such:\n# obj = CombinationIterator.new(characters, combination_length)\n# param_1 = obj.next()\n# param_2 = obj.has_next()"}, {"value": "scala", "text": "Scala", "defaultCode": "class CombinationIterator(_characters: String, _combinationLength: Int) {\n\n    def next(): String = {\n        \n    }\n\n    def hasNext(): Boolean = {\n        \n    }\n\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * val obj = new CombinationIterator(characters, combinationLength)\n * val param_1 = obj.next()\n * val param_2 = obj.hasNext()\n */"}, {"value": "rust", "text": "Rust", "defaultCode": "struct CombinationIterator {\n\n}\n\n\n/** \n * `&self` means the method takes an immutable reference.\n * If you need a mutable reference, change it to `&mut self` instead.\n */\nimpl CombinationIterator {\n\n    fn new(characters: String, combinationLength: i32) -> Self {\n        \n    }\n    \n    fn next(&self) -> String {\n        \n    }\n    \n    fn has_next(&self) -> bool {\n        \n    }\n}\n\n/**\n * Your CombinationIterator object will be instantiated and called as such:\n * let obj = CombinationIterator::new(characters, combinationLength);\n * let ret_1: String = obj.next();\n * let ret_2: bool = obj.has_next();\n */"}, {"value": "racket", "text": "Racket", "defaultCode": "(define combination-iterator%\n  (class object%\n    (super-new)\n    \n    ; characters : string?\n    ; combination-length : exact-integer?\n    (init-field\n      characters\n      combination-length)\n    \n    ; next : -> string?\n    (define/public (next)\n      )\n    ; has-next : -> boolean?\n    (define/public (has-next)\n      )))\n\n;; Your combination-iterator% object will be instantiated and called as such:\n;; (define obj (new combination-iterator% [characters characters] [combination-length combination-length]))\n;; (define param_1 (send obj next))\n;; (define param_2 (send obj has-next))"}, {"value": "erlang", "text": "Erlang", "defaultCode": "-spec combination_iterator_init_(Characters :: unicode:unicode_binary(), CombinationLength :: integer()) -> any().\ncombination_iterator_init_(Characters, CombinationLength) ->\n  .\n\n-spec combination_iterator_next() -> unicode:unicode_binary().\ncombination_iterator_next() ->\n  .\n\n-spec combination_iterator_has_next() -> boolean().\ncombination_iterator_has_next() ->\n  .\n\n\n%% Your functions will be called as such:\n%% combination_iterator_init_(Characters, CombinationLength),\n%% Param_1 = combination_iterator_next(),\n%% Param_2 = combination_iterator_has_next(),\n\n%% combination_iterator_init_ will be called before every test case, in which you can do some necessary initializations."}, {"value": "elixir", "text": "Elixir", "defaultCode": "defmodule CombinationIterator do\n  @spec init_(characters :: String.t, combination_length :: integer) :: any\n  def init_(characters, combination_length) do\n    \n  end\n\n  @spec next() :: String.t\n  def next() do\n    \n  end\n\n  @spec has_next() :: boolean\n  def has_next() do\n    \n  end\nend\n\n# Your functions will be called as such:\n# CombinationIterator.init_(characters, combination_length)\n# param_1 = CombinationIterator.next()\n# param_2 = CombinationIterator.has_next()\n\n# CombinationIterator.init_ will be called before every test case, in which you can do some necessary initializations."}]
{
  "classname": "CombinationIterator",
  "maxbytesperline": 200000,
  "constructor": {
    "params": [
      {
        "type": "string",
        "name": "characters"
      },
      {
        "type": "integer",
        "name": "combinationLength"
      }
    ]
  },
  "methods": [
    {
      "name": "next",
      "params": [],
      "return": {
        "type": "string"
      }
    },
    {
      "name": "hasNext",
      "params": [],
      "return": {
        "type": "boolean"
      }
    }
  ],
  "systemdesign": true,
  "params": [
    {
      "name": "inputs",
      "type": "integer[]"
    },
    {
      "name": "inputs",
      "type": "integer[]"
    }
  ],
  "return": {
    "type": "list<String>",
    "dealloc": true
  }
}
{"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', 'Design', 'Iterator']