206. Reverse Linked List

# 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]:
        if not head or not head.next:
            return head

        prev = current = head
        nextNode = head.next
        while current and nextNode:
            current = nextNode
            nextNode = current.next
            current.next = prev
            prev = current

        head.next = None

        return prev