Reorder List

You are given the head of a singly linked-list. The list can be represented as:

L0 -> L1 -> ... -> Ln - 1 -> Ln

Reorder the list to be on the following form:

L0 -> Ln -> L1 -> Ln - 1 -> L2 -> Ln - 2 -> ...

You may not modify the values in the list's nodes. Only nodes themselves may be changed.

Example 1:

Input: head = [1,2,3,4] Output: [1,4,2,3]

Example 2:

Input: head = [1,2,3,4,5] Output: [1,5,2,4,3]

Constraints:

• The number of nodes in the list is in the range [1, 5 * 104].
• 1 <= Node.val <= 1000