1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 5         :rtype: ListNode
 6         """
 7         
 8         n = self.getLength(headA)
 9         m = self.getLength(headB)
10         
11         if n < m:
12             return self.getIntersectionNode(headB, headA)
13         
14         for i in range(n-m):
15             headA = headA.next
16         
17         while headA and headB:
18             if id(headA) == id(headB):
19                 return headA
20             headA = headA.next
21             headB = headB.next
22         return None
23     
24     def getLength(self, head):
25         n = 0
26         while head:
27             head = head.next
28             n += 1
29         return n