PYTHON

reverse sublist of linklist

    def reverseBetween(self, head: Optional[ListNode], left: int, right: int) -> Optional[ListNode]:
        def reverse(head):
            prev = None
            cur = head
            while cur:
                nxt = cur.next
                cur.next = prev
                prev = cur
                cur = nxt
            return prev
        if left == right:
            return head
        start = None
        startp = None
        end = None
        endn = None
        count = 1
        cur = head
        while cur and count <= right:
            if count < left:
                startp = cur
            if count == left:
                start = cur
            if count == right:
                end = cur
                endn = cur.next
            cur = cur.next
            count += 1
        end.next = None
        end = reverse(start)
        if startp:
            startp.next = end
        else:
            head = end
        start.next = endn
        return head