Given the head of a singly linked list L0 → L1 → … → Ln-1 → Ln , reorder it in place to L0 → Ln → L1 → Ln-1 → L2 → Ln-2 → … . You may not change the node values — only the links. Input format Input is [list] , e.g. [[1,2,3,4]] . The reference mutates the list in place; the harness reads back the reordered list from the (mutated) argument. ListNode is predefined.