输入两个单向链表，找出它们的第一个公共结点

题目：
解答：
 1 public class Solution {
 2 
 3 
 4     public static void main(String[] args) {
 5         ListNode head1 = new ListNode();
 6         ListNode second1 = new ListNode();
 7         ListNode third1 = new ListNode();
 8         ListNode forth1 = new ListNode();
 9         ListNode fifth1 = new ListNode();
10         ListNode head2 = new ListNode();
11         ListNode second2 = new ListNode();
12         ListNode third2 = new ListNode();
13         ListNode forth2 = new ListNode();
14         head1.nextNode = second1;
15         second1.nextNode = third1;
16         third1.nextNode = forth1;
17         forth1.nextNode = fifth1;
18         head2.nextNode = second2;
19         second2.nextNode = forth1;
20         third2.nextNode = fifth1;
21         head1.data = 1;
22         second1.data = 2;
23         third1.data = 3;
24         forth1.data = 6;
25         fifth1.data = 7;
26         head2.data = 4;
27         second2.data = 5;
28         third2.data = 6;
29         forth2.data = 7;
30         System.out.println(findFirstCommonNode(head1,head2).data);
31         
32     }
33 
34     public static ListNode findFirstCommonNode(ListNode head1, ListNode head2) {
35         int len1 = getListLength(head1);
36         int len2 = getListLength(head2);
37 
38         ListNode longListNode = null;
39         ListNode shortListNode = null;
40 
41         int diff = 0;
42         if(len1 > len2) {
43             longListNode = head1;
44             shortListNode = head2;
45             diff = len1 - len2;
46         } else {
47             longListNode = head2;
48             shortListNode = head1;
49             diff = len2 - len1;
50         }
51 
52         for(int i = 0; i < diff; i++) {
53             longListNode = longListNode.nextNode;
54         }
55 
56         while(longListNode != null && shortListNode != null && longListNode != shortListNode) {
57             longListNode = longListNode.nextNode;
58             shortListNode = shortListNode.nextNode;
59         }
60 
61         return longListNode;
62     }
63 
64 
65 
66     private static int getListLength(ListNode head) {
67         int result = 0;
68         if(head == null) {
69             return result;
70         }
71 
72         ListNode point = head;
73         while(point != null) {
74             point = point.nextNode;
75             result++;
76         }
77 
78         return result;
79     }
80 }
81 
82 
83 public class ListNode {
84     int data;
85     ListNode nextnode;
86 }