leetcode 【 Intersection of Two Linked Lists 】python 实现

题目：

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.

代码：oj在线测试通过 Runtime: 1604 ms

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

 class Solution:
     # @param two ListNodes
     # @return the intersected ListNode
     def getListLen(self,head):
         length = 0
         while head is not None:
             length += 1
             head = head.next
         return length

     def getIntersectionNode(self, headA, headB):
         if headA is None or headB is None:
             return None

         hA = headA
         hB = headB

         lenA = self.getListLen(hA)
         lenB = self.getListLen(hB)

         if lenA > lenB :
             distance = lenA - lenB
             for i in range(0,distance):
                 hA = hA.next
         if lenA < lenB :
             distance = lenB -lenA
             for i in range(0,distance):
                 hB = hB.next

         intersection = None
         while hA is not None and hB is not None:
             if hA == hB:
                 return hA
             else:
                 hA = hA.next
                 hB = hB.next
         return intersection

思路：

1. 首先要记录两个Linked List的长度

2. 双指针 分别指向两个List 指向长List的先走若干步,获得一个新的Linked List表头

3. 逐一比较两个List的每个指针的值是否相等：直到找到相等的，或者到None