Maximum Twin Sum of a Linked List

Statement

In a linked list of even length $n$, the node at position $i$ (0-based indexing) is considered the twin of the node at position $(n-1-i)$ for all $0 ≤ i < n/2$. For example, if $n=4$, node $0$ and node $3$ are twins, and node $1$ and node $2$ are twins. These pairs are the only twins in a linked list of size $4$.

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

Given the head of a linked list with an even number of nodes, return the maximum twin sum of the linked list.

Constraints:

• The list contains an even number of nodes in the range $[2, 10^3]$.

• $1 \leq$ Node.value $\leq 10^3$

Examples