reorderList = function(head) {
    const mid = getMid(head);           /* Time O(N) */
    const reversedFromMid = reverse(mid);/* Time O(N) */

    reorder(head, reversedFromMid);      /* Time O(N) */
}
https://leetcode.com/problems/reorder-list/
Time O(N) | Space O(1)
@param {ListNode} head
@return {void} Do not return anything, modify head in-place instead.