# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
       prev = None
       curr = head
       while curr:
           temp = curr.next
           curr.next = prev
           
           prev = curr
           curr = temp

       return prev
