{ "data": { "question": { "questionId": "2236", "questionFrontendId": "2130", "boundTopicId": null, "title": "Maximum Twin Sum of a Linked List", "titleSlug": "maximum-twin-sum-of-a-linked-list", "content": "

In a linked list of size n, where n is even, the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node, if 0 <= i <= (n / 2) - 1.

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The twin sum is defined as the sum of a node and its twin.

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Given the head of a linked list with even length, return the maximum twin sum of the linked list.

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Example 1:

\n\"\"\n
\nInput: head = [5,4,2,1]\nOutput: 6\nExplanation:\nNodes 0 and 1 are the twins of nodes 3 and 2, respectively. All have twin sum = 6.\nThere are no other nodes with twins in the linked list.\nThus, the maximum twin sum of the linked list is 6. \n
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Example 2:

\n\"\"\n
\nInput: head = [4,2,2,3]\nOutput: 7\nExplanation:\nThe nodes with twins present in this linked list are:\n- Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7.\n- Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4.\nThus, the maximum twin sum of the linked list is max(7, 4) = 7. \n
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Example 3:

\n\"\"\n
\nInput: head = [1,100000]\nOutput: 100001\nExplanation:\nThere is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001.\n
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Constraints:

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0 : val)\n * this.next = (next===undefined ? null : next)\n * }\n */\n/**\n * @param {ListNode} head\n * @return {number}\n */\nvar pairSum = function(head) {\n \n};", "__typename": "CodeSnippetNode" }, { "lang": "TypeScript", "langSlug": "typescript", "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 pairSum(head: ListNode | null): number {\n \n};", "__typename": "CodeSnippetNode" }, { "lang": "PHP", "langSlug": "php", "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 $head\n * @return Integer\n */\n function pairSum($head) {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "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 pairSum(_ head: ListNode?) -> Int {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "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 pairSum(head: ListNode?): Int {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Dart", "langSlug": "dart", "code": "/**\n * Definition for singly-linked list.\n * class ListNode {\n * int val;\n * ListNode? next;\n * ListNode([this.val = 0, this.next]);\n * }\n */\nclass Solution {\n int pairSum(ListNode? head) {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Go", "langSlug": "golang", "code": "/**\n * Definition for singly-linked list.\n * type ListNode struct {\n * Val int\n * Next *ListNode\n * }\n */\nfunc pairSum(head *ListNode) int {\n \n}", "__typename": "CodeSnippetNode" }, { "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# @return {Integer}\ndef pair_sum(head)\n \nend", "__typename": "CodeSnippetNode" }, { "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 pairSum(head: ListNode): Int = {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "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>\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 pair_sum(head: Option>) -> i32 {\n \n }\n}", "__typename": "CodeSnippetNode" }, { "lang": "Racket", "langSlug": "racket", "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 (pair-sum head)\n (-> (or/c list-node? #f) exact-integer?)\n )", "__typename": "CodeSnippetNode" }, { "lang": "Erlang", "langSlug": "erlang", "code": "%% Definition for singly-linked list.\n%%\n%% -record(list_node, {val = 0 :: integer(),\n%% next = null :: 'null' | #list_node{}}).\n\n-spec pair_sum(Head :: #list_node{} | null) -> integer().\npair_sum(Head) ->\n .", "__typename": "CodeSnippetNode" }, { "lang": "Elixir", "langSlug": "elixir", "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 pair_sum(head :: ListNode.t | nil) :: integer\n def pair_sum(head) do\n \n end\nend", "__typename": "CodeSnippetNode" } ], "stats": "{\"totalAccepted\": \"219.4K\", \"totalSubmission\": \"269.4K\", \"totalAcceptedRaw\": 219383, \"totalSubmissionRaw\": 269438, \"acRate\": \"81.4%\"}", "hints": [ "How can \"reversing\" a part of the linked list help find the answer?", "We know that the nodes of the first half are twins of nodes in the second half, so try dividing the linked list in half and reverse the second half.", "How can two pointers be used to find every twin sum optimally?", "Use two different pointers pointing to the first nodes of the two halves of the linked list. 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