两个链表的第一个公共结点

题目描述

输入两个链表，找出它们的第一个公共结点。
 1 import java.util.HashSet;
 2 import java.util.Set;
 3 
 4 /**
 5  * 
 6  * @author gentleKay
 7  * 题目描述
 8  * 输入两个链表，找出它们的第一个公共结点。
 9  */
10 
11 public class Main35 {
12     public static void main(String[] args) {
13         ListNode head1 = new ListNode(1);
14         head1.next = new ListNode(2);
15         head1.next.next = new ListNode(3);
16         head1.next.next.next = new ListNode(6);
17         head1.next.next.next.next = new ListNode(7);
18         
19         ListNode head2 = new ListNode(4);
20         head2.next = new ListNode(5);
21         head2.next.next = new ListNode(6);
22         head2.next.next.next = new ListNode(7);
23         
24         System.out.println(Main35.FindFirstCommonNode(head1, head2));
25         
26 //        ListNode root = Main35.FindFirstCommonNode(head1, head2);
27 //        System.out.println(root.val);
28     }
29     
30     public static class ListNode {
31         int val;
32         ListNode next = null;
33 
34         ListNode(int val) {
35             this.val = val;
36         }
37     }
38     
39     public static ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
40         
41         ListNode node1 = pHead1;
42         ListNode node2 = pHead2;
43         
44         Set<ListNode> hashSet = new HashSet<>();
45         while (node1 != null) {
46             hashSet.add(node1);
47             node1 = node1.next;
48         }
49         while (node2 != null) {
50             if (hashSet.contains(node2)) {
51                 return node2;
52             }
53             node2 = node2.next;
54         }
55         return null;
56     }
57 }