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            "title": "Reverse Nodes in k-Group",
            "titleSlug": "reverse-nodes-in-k-group",
            "content": "<p>Given the <code>head</code> of a linked list, reverse the nodes of the list <code>k</code> at a time, and return <em>the modified list</em>.</p>\n\n<p><code>k</code> is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of <code>k</code> then left-out nodes, in the end, should remain as it is.</p>\n\n<p>You may not alter the values in the list&#39;s nodes, only nodes themselves may be changed.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/10/03/reverse_ex1.jpg\" style=\"width: 542px; height: 222px;\" />\n<pre>\n<strong>Input:</strong> head = [1,2,3,4,5], k = 2\n<strong>Output:</strong> [2,1,4,3,5]\n</pre>\n\n<p><strong>Example 2:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/10/03/reverse_ex2.jpg\" style=\"width: 542px; height: 222px;\" />\n<pre>\n<strong>Input:</strong> head = [1,2,3,4,5], k = 3\n<strong>Output:</strong> [3,2,1,4,5]\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li>The number of nodes in the list is <code>n</code>.</li>\n\t<li><code>1 &lt;= k &lt;= n &lt;= 5000</code></li>\n\t<li><code>0 &lt;= Node.val &lt;= 1000</code></li>\n</ul>\n\n<p>&nbsp;</p>\n<p><strong>Follow-up:</strong> Can you solve the problem in <code>O(1)</code> extra memory space?</p>\n",
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            "exampleTestcases": "[1,2,3,4,5]\n2\n[1,2,3,4,5]\n3",
            "categoryTitle": "Algorithms",
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            "topicTags": [
                {
                    "name": "Linked List",
                    "slug": "linked-list",
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                    "name": "Recursion",
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                    "lang": "C++",
                    "langSlug": "cpp",
                    "code": "/**\n * Definition for singly-linked list.\n * struct ListNode {\n *     int val;\n *     ListNode *next;\n *     ListNode() : val(0), next(nullptr) {}\n *     ListNode(int x) : val(x), next(nullptr) {}\n *     ListNode(int x, ListNode *next) : val(x), next(next) {}\n * };\n */\nclass Solution {\npublic:\n    ListNode* reverseKGroup(ListNode* head, int k) {\n        \n    }\n};",
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                {
                    "lang": "Java",
                    "langSlug": "java",
                    "code": "/**\n * Definition for singly-linked list.\n * public class ListNode {\n *     int val;\n *     ListNode next;\n *     ListNode() {}\n *     ListNode(int val) { this.val = val; }\n *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }\n * }\n */\nclass Solution {\n    public ListNode reverseKGroup(ListNode head, int k) {\n        \n    }\n}",
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                {
                    "lang": "Python",
                    "langSlug": "python",
                    "code": "# Definition for singly-linked list.\n# class ListNode(object):\n#     def __init__(self, val=0, next=None):\n#         self.val = val\n#         self.next = next\nclass Solution(object):\n    def reverseKGroup(self, head, k):\n        \"\"\"\n        :type head: ListNode\n        :type k: int\n        :rtype: ListNode\n        \"\"\"\n        ",
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                    "lang": "Python3",
                    "langSlug": "python3",
                    "code": "# Definition for singly-linked list.\n# class ListNode:\n#     def __init__(self, val=0, next=None):\n#         self.val = val\n#         self.next = next\nclass Solution:\n    def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:\n        ",
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                {
                    "lang": "C",
                    "langSlug": "c",
                    "code": "/**\n * Definition for singly-linked list.\n * struct ListNode {\n *     int val;\n *     struct ListNode *next;\n * };\n */\n\n\nstruct ListNode* reverseKGroup(struct ListNode* head, int k){\n\n}",
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                    "lang": "C#",
                    "langSlug": "csharp",
                    "code": "/**\n * Definition for singly-linked list.\n * public class ListNode {\n *     public int val;\n *     public ListNode next;\n *     public ListNode(int val=0, ListNode next=null) {\n *         this.val = val;\n *         this.next = next;\n *     }\n * }\n */\npublic class Solution {\n    public ListNode ReverseKGroup(ListNode head, int k) {\n        \n    }\n}",
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                {
                    "lang": "JavaScript",
                    "langSlug": "javascript",
                    "code": "/**\n * Definition for singly-linked list.\n * function ListNode(val, next) {\n *     this.val = (val===undefined ? 0 : val)\n *     this.next = (next===undefined ? null : next)\n * }\n */\n/**\n * @param {ListNode} head\n * @param {number} k\n * @return {ListNode}\n */\nvar reverseKGroup = function(head, k) {\n    \n};",
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                {
                    "lang": "Ruby",
                    "langSlug": "ruby",
                    "code": "# Definition for singly-linked list.\n# class ListNode\n#     attr_accessor :val, :next\n#     def initialize(val = 0, _next = nil)\n#         @val = val\n#         @next = _next\n#     end\n# end\n# @param {ListNode} head\n# @param {Integer} k\n# @return {ListNode}\ndef reverse_k_group(head, k)\n    \nend",
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                {
                    "lang": "Swift",
                    "langSlug": "swift",
                    "code": "/**\n * Definition for singly-linked list.\n * public class ListNode {\n *     public var val: Int\n *     public var next: ListNode?\n *     public init() { self.val = 0; self.next = nil; }\n *     public init(_ val: Int) { self.val = val; self.next = nil; }\n *     public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }\n * }\n */\nclass Solution {\n    func reverseKGroup(_ head: ListNode?, _ k: Int) -> ListNode? {\n        \n    }\n}",
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                {
                    "lang": "Go",
                    "langSlug": "golang",
                    "code": "/**\n * Definition for singly-linked list.\n * type ListNode struct {\n *     Val int\n *     Next *ListNode\n * }\n */\nfunc reverseKGroup(head *ListNode, k int) *ListNode {\n    \n}",
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                    "lang": "Scala",
                    "langSlug": "scala",
                    "code": "/**\n * Definition for singly-linked list.\n * class ListNode(_x: Int = 0, _next: ListNode = null) {\n *   var next: ListNode = _next\n *   var x: Int = _x\n * }\n */\nobject Solution {\n    def reverseKGroup(head: ListNode, k: Int): ListNode = {\n        \n    }\n}",
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                    "lang": "Kotlin",
                    "langSlug": "kotlin",
                    "code": "/**\n * Example:\n * var li = ListNode(5)\n * var v = li.`val`\n * Definition for singly-linked list.\n * class ListNode(var `val`: Int) {\n *     var next: ListNode? = null\n * }\n */\nclass Solution {\n    fun reverseKGroup(head: ListNode?, k: Int): ListNode? {\n        \n    }\n}",
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                    "lang": "Rust",
                    "langSlug": "rust",
                    "code": "// Definition for singly-linked list.\n// #[derive(PartialEq, Eq, Clone, Debug)]\n// pub struct ListNode {\n//   pub val: i32,\n//   pub next: Option<Box<ListNode>>\n// }\n// \n// impl ListNode {\n//   #[inline]\n//   fn new(val: i32) -> Self {\n//     ListNode {\n//       next: None,\n//       val\n//     }\n//   }\n// }\nimpl Solution {\n    pub fn reverse_k_group(head: Option<Box<ListNode>>, k: i32) -> Option<Box<ListNode>> {\n        \n    }\n}",
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                    "lang": "PHP",
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                    "code": "/**\n * Definition for a singly-linked list.\n * class ListNode {\n *     public $val = 0;\n *     public $next = null;\n *     function __construct($val = 0, $next = null) {\n *         $this->val = $val;\n *         $this->next = $next;\n *     }\n * }\n */\nclass Solution {\n\n    /**\n     * @param ListNode $head\n     * @param Integer $k\n     * @return ListNode\n     */\n    function reverseKGroup($head, $k) {\n        \n    }\n}",
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                    "lang": "TypeScript",
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                    "code": "/**\n * Definition for singly-linked list.\n * class ListNode {\n *     val: number\n *     next: ListNode | null\n *     constructor(val?: number, next?: ListNode | null) {\n *         this.val = (val===undefined ? 0 : val)\n *         this.next = (next===undefined ? null : next)\n *     }\n * }\n */\n\nfunction reverseKGroup(head: ListNode | null, k: number): ListNode | null {\n\n};",
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                    "lang": "Racket",
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                    "code": "; Definition for singly-linked list:\n#|\n\n; val : integer?\n; next : (or/c list-node? #f)\n(struct list-node\n  (val next) #:mutable #:transparent)\n\n; constructor\n(define (make-list-node [val 0])\n  (list-node val #f))\n\n|#\n\n(define/contract (reverse-k-group head k)\n  (-> (or/c list-node? #f) exact-integer? (or/c list-node? #f))\n\n  )",
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                    "lang": "Erlang",
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                    "code": "%% Definition for singly-linked list.\n%%\n%% -record(list_node, {val = 0 :: integer(),\n%%                     next = null :: 'null' | #list_node{}}).\n\n-spec reverse_k_group(Head :: #list_node{} | null, K :: integer()) -> #list_node{} | null.\nreverse_k_group(Head, K) ->\n  .",
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                    "lang": "Elixir",
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                    "code": "# Definition for singly-linked list.\n#\n# defmodule ListNode do\n#   @type t :: %__MODULE__{\n#           val: integer,\n#           next: ListNode.t() | nil\n#         }\n#   defstruct val: 0, next: nil\n# end\n\ndefmodule Solution do\n  @spec reverse_k_group(head :: ListNode.t | nil, k :: integer) :: ListNode.t | nil\n  def reverse_k_group(head, k) do\n\n  end\nend",
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