class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
class LinkedList:
    def __init__(self, head=None):
        self.head = head
    def reverse(self):
        if self.head == None or self.head.next == None:
            return
        prev = None
        ahead = self.head.next
        while ahead:
            self.head.next = prev
            prev = self.head
            self.head = ahead
            ahead = ahead.next
        self.head.next = prev
class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        linkedlist = LinkedList(head)
        linkedlist.reverse()
        return linkedlist.head