# 160. Intersection of Two Linked Lists 相交链表

@TOC

## # 题目描述

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

``````A:          a1 → a2
↘
c1 → c2 → c3
↗
B:     b1 → b2 → b3
begin to intersect at node c1.
``````

Notes:

1. If the two linked lists have no intersection at all, return null.
2. The linked lists must retain their original structure after the function returns.
3. You may assume there are no cycles anywhere in the entire linked structure.
4. Your code should preferably run in O(n) time and use only O(1) memory. Credits:
5. Special thanks to @stellari for adding this problem and creating all test cases.

## # 解题方法

### # 双指针

``````# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
"""
:rtype: ListNode
"""
if headA is None or headB is None:
return None
while pA is not pB:
pA = headB if pA is None else pA.next
pB = headA if pB is None else pB.next
return pA
``````

``````# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
"""
:rtype: ListNode
"""
len1, len2 = 0, 0
while moveA:
len1 += 1
moveA = moveA.next
while moveB:
len2 += 1
moveB = moveB.next
if len1 < len2:
for _ in range(len2 - len1):
else:
for _ in range(len1 - len2):
``````

### # 栈

``````# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
"""
:rtype: ListNode
"""
stack1, stack2 = [], []
pre = None
while stack1 and stack2:
s1 = stack1.pop()
s2 = stack2.pop()
if s1 != s2:
return pre
else:
pre = s1
return pre
``````

## # 日期

2017 年 8 月 27 日 2018 年 11 月 26 日 —— 11月最后一周！