leetcode--Intersection of Two Linked Lists

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:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns.
• You may assume there are no cycles anywhere in the entire linked structure.
• Your code should preferably run in O(n) time and use only O(1) memory.

[java]  view plain  copy

1. /** 
2.  * Definition for singly-linked list. 
3.  * public class ListNode { 
4.  *     int val; 
5.  *     ListNode next; 
6.  *     ListNode(int x) { 
7.  *         val = x; 
8.  *         next = null; 
9.  *     } 
10.  * } 
11.  */  
12. public class Solution {  
13.     public ListNode getIntersectionNode(ListNode headA, ListNode headB) {  
14.         if(headA == null ||headB == null)return null;    
15.         ListNode h1 = headA;    
16.         ListNode h2 = headB;    
17.         int count1 = 1, count2 = 1;    
18.         while(h1.next != null){    
19.             count1++;    
20.             h1 = h1.next;    
21.         }    
22.         while(h2.next != null){    
23.             count2++;    
24.             h2 = h2.next;    
25.         }    
26.         if(h1 != h2) return null;    
27.         else{    
28.             int count = Math.abs(count1 - count2);    
29.             if(count2 > count1){    
30.                 h1 = headB;    
31.                 h2 = headA;     
32.             }    
33.             else{    
34.                 h1 = headA;    
35.                 h2 = headB;    
36.             }    
37.             while((count--) > 0){    
38.                 h1 = h1.next;    
39.             }    
40.             while(h1 != null&&h2 != null && h1 != h2){    
41.                 h1 = h1.next;    
42.                 h2 = h2.next;    
43.             }    
44.             return h1;    
45.         }    
46.     }  
47. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/46383675