LeetCode Entry

2130. Maximum Twin Sum of a Linked List

14.06.2026 medium 2026 kotlin rust

Max sum pairwise from tail

2130. Maximum Twin Sum of a Linked List medium substack youtube

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Problem TLDR

Max sum pairwise from tail

Intuition

Put into a list or revert the first half.

Approach

• Kotlin: generateSequence
• Rust: from_fn

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(n|1)\)

Code

    fun pairSum(h: ListNode?) =
        generateSequence(h){it.next}.map{it.`val`}
        .toList().run {zip(reversed(), Int::plus).max()}

    pub fn pair_sum(mut h: Option<Box<ListNode>>) -> i32 {
       let l: Vec<_> = from_fn(||h.take().map(|n|{h=n.next; n.val})).collect();
       l.iter().rev().zip(&l).map(|(a,b)|a+b).max().unwrap()
    }