leetcode92

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def reverseBetween(self, head, left, right):
        """
        :type head: ListNode
        :type left: int
        :type right: int
        :rtype: ListNode
        """
        if left==right:return head
        aptr=head
        m=1
        h1=None
        h2=None 
        while aptr!=None:
            if m==left:
                h1=aptr
            if m==right:
                h2=aptr
            aptr=aptr.next
            m+=1
        h3=h2.next
        h2.next=None 
        h4=self.reverseList(h1)
        aptr=h2
        while aptr.next!=None:
            if aptr.next==h2:
                break
            aptr=aptr.next
        if h3!=None:
            aptr.next=h3
        if left>1:
            aptr=head

        while  aptr!=None:
            if aptr.next==h1:
                break 
            aptr=aptr.next
        if aptr!=None:
            aptr.next=h2
        else:
            head=h2
        return head

    def reverseList(self,aptr):
        if aptr.next==None:return aptr
        last=self.reverseList(aptr.next)
        aptr.next.next=aptr
        aptr.next=None
        return last