class Solution:
    def reverseBetween(self, head: ListNode, left: int, right: int) -> ListNode:
        dummy=ListNode(val=None,next=head)
        curr1=curr2=dummy
        for _ in range(right):
            curr2=curr2.next

        for _ in range(left-1):
            curr1=curr1.next

        for _ in range(right-left):
            tmp=curr1.next
            curr1.next=curr1.next.next
            tmp.next=curr2.next
            curr2.next=tmp

        return dummy.next

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        if head is None:
            return None
        dummy = ListNode(val=None,next=head)

        curr=dummy
        while curr.next:
            curr=curr.next

        while dummy.next is not curr:
            tmp=dummy.next
            dummy.next=dummy.next.next
            tmp.next=curr.next
            curr.next=tmp

        return dummy.next

class Solution:
    def reverseList(self, head):
        p, rev = head, None
        while p:
            rev, rev.next, p = p, rev, p.next
        return rev