reverseList = function (head) {
    const isBaseCase = !head?.next;
    if (isBaseCase) return head;

    return dfs(head);                   /* Time O(N) | Space O(N) */
}
https://leetcode.com/problems/reverse-linked-list/
Time O(N) | Space O(N)
@param {ListNode} head
@return {ListNode}