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。

import java.util.HashSet;
import java.util.Set;

/**
 * 
 * @author gentleKay
 * 题目描述
 * 输入两个链表，找出它们的第一个公共结点。
 */

public class Main35 {
    public static void main(String[] args) {
        ListNode head1 = new ListNode(1);
        head1.next = new ListNode(2);
        head1.next.next = new ListNode(3);
        head1.next.next.next = new ListNode(6);
        head1.next.next.next.next = new ListNode(7);
        
        ListNode head2 = new ListNode(4);
        head2.next = new ListNode(5);
        head2.next.next = new ListNode(6);
        head2.next.next.next = new ListNode(7);
        
        System.out.println(Main35.FindFirstCommonNode(head1, head2));
        
//        ListNode root = Main35.FindFirstCommonNode(head1, head2);
//        System.out.println(root.val);
    }
    
    public static class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }
    
    public static ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        
        ListNode node1 = pHead1;
        ListNode node2 = pHead2;
        
        Set<ListNode> hashSet = new HashSet<>();
        while (node1 != null) {
            hashSet.add(node1);
            node1 = node1.next;
        }
        while (node2 != null) {
            if (hashSet.contains(node2)) {
                return node2;
            }
            node2 = node2.next;
        }
        return null;
    }
}