package main

type ListNode struct {
	Val  int
	Next *ListNode
}

func main() {

}
func reverseList(head *ListNode) *ListNode {
	pre := (*ListNode)(nil)
	res := (*ListNode)(nil)
	for head != nil {
		next := head.Next
		head.Next = pre
		pre = head
		if next == nil {
			res = head
			break
		}
		head = next
	}
	return res
}