In a linked list of size
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.
- For example, if
n = 4, then node
0is the twin of node
3, and node
1is the twin of node
2. These are the only nodes with twins for
n = 4.
The twin sum is defined as the sum of a node and its twin.
head of a linked list with even length, return the maximum twin sum of the linked list.
(5) ->  ->  -> (1) Input: head = [5,4,2,1] Output: 6 Explanation: Nodes 0 and 1 are the twins of nodes 3 and 2, respectively. All have twin sum = 6. There are no other nodes with twins in the linked list. Thus, the maximum twin sum of the linked list is 6.
(4) ->  ->  -> (3) Input: head = [4,2,2,3] Output: 7 Explanation: The nodes with twins present in this linked list are: - Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7. - Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4. Thus, the maximum twin sum of the linked list is max(7, 4) = 7.
(1) -> (100000) Input: head = [1,100000] Output: 100001 Explanation: There is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001.
- The number of nodes in the list is an even integer in the range
1 <= Node.val <= 105