/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reverseList(head *ListNode) *ListNode {
	return reverseRecurse(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) *ListNode {
	if head == nil || head.Next == nil {
		return head
	}
	newHead := reverseRecurse(head.Next)
	head.Next.Next = head
	head.Next = nil
	return newHead
}