/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reverseList(head *ListNode) *ListNode {
	reverseRecurse(&head)
	return head
// return reverseIter(head, nil)
}

func reverseIter(head, tail *ListNode) *ListNode {
	if head == nil {
		return tail
	}
	curr := head
	head = head.Next
	curr.Next = tail
	return reverseIter(head, curr)
}

func reverseRecurse(head **ListNode) {
	first := *head
	if first == nil {
		return
	}
	rest := first.Next
	if rest == nil {
		return
	}
	reverseRecurse(&rest)
	first.Next.Next = first
	first.Next = nil
	*head = rest
}