1+ # Given the heads of two singly linked-lists headA and headB, return the node
2+ # at which the two lists intersect. If the two linked lists have no intersection
3+ # at all, return null.
4+ 5+ # For example, the following two linked lists begin to intersect at node c1:
6+ 7+ 8+ # The test cases are generated such that there are no cycles anywhere in the
9+ # entire linked structure.
10+ 11+ # Note that the linked lists must retain their original structure after the
12+ # function returns.
13+ 14+ # Custom Judge:
15+ # The inputs to the judge are given as follows (your program is not given these inputs):
16+ 17+ # intersectVal - The value of the node where the intersection occurs. This is 0 if
18+ # there is no intersected node.
19+ 20+ # listA - The first linked list.
21+ # listB - The second linked list.
22+ # skipA - The number of nodes to skip ahead in listA (starting from the head) to get
23+ # to the intersected node.
24+ # skipB - The number of nodes to skip ahead in listB (starting from the head) to get
25+ # to the intersected node.
26+ # The judge will then create the linked structure based on these inputs and pass the
27+ # two heads, headA and headB to your program. If you correctly return the intersected
28+ # node, then your solution will be accepted.
29+ 30+ 31+ # Example 1:
32+ # Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,6,1,8,4,5], skipA = 2, skipB = 3
33+ # Output: Intersected at '8'
34+ # Explanation: The intersected node's value is 8 (note that this must not be 0 if the two
35+ # lists intersect).
36+ # From the head of A, it reads as [4,1,8,4,5]. From the head of B, it reads as [5,6,1,8,4,5].
37+ # There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B.
38+ # - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B
39+ # (2nd node in A and 3rd node in B) are different node references. In other words, they point
40+ # to two different locations in memory, while the nodes with value 8 in A and B
41+ # (3rd node in A and 4th node in B) point to the same location in memory.
42+ 43+ # Example 2:
44+ # Input: intersectVal = 2, listA = [1,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
45+ # Output: Intersected at '2'
46+ # Explanation: The intersected node's value is 2 (note that this must not be 0 if the
47+ # two lists intersect).
48+ # From the head of A, it reads as [1,9,1,2,4]. From the head of B, it reads as [3,2,4].
49+ # There are 3 nodes before the intersected node in A; There are 1 node before the intersected
50+ # node in B.
51+ 52+ # Example 3:
53+ # Input: intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
54+ # Output: No intersection
55+ # Explanation: From the head of A, it reads as [2,6,4]. From the head of B, it reads as [1,5].
56+ # Since the two lists do not intersect, intersectVal must be 0, while skipA and skipB can be
57+ # arbitrary values.
58+ # Explanation: The two lists do not intersect, so return null.
59+ 60+ 61+ # Constraints:
62+ 63+ # The number of nodes of listA is in the m.
64+ # The number of nodes of listB is in the n.
65+ # 1 <= m, n <= 3 * 104
66+ # 1 <= Node.val <= 105
67+ # 0 <= skipA <= m
68+ # 0 <= skipB <= n
69+ # intersectVal is 0 if listA and listB do not intersect.
70+ # intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect.
71+ 72+ 73+ 74+ from typing import Optional
75+ 76+ # Definition for singly-linked list.
77+ class ListNode :
78+ def __init__ (self , x ):
79+ self .val = x
80+ self .next = None
81+ 82+ class Solution :
83+ def getIntersectionNode (self , headA : ListNode , headB : ListNode ) -> Optional [ListNode ]:
84+ a = headA
85+ b = headB
86+ 87+ while a != b :
88+ a = a .next if a else headB
89+ b = b .next if b else headA
90+ return a
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