剑指offer七：两个链表的第一个公共结点

输入两个链表，找出它们的第一个公共结点。

import java.util.*;
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
         ListNode current1 = pHead1;
        ListNode current2 = pHead2;

       HashMap<ListNode,Integer> hashMap = new HashMap<ListNode,Integer>();

        while(current1 != null){
            hashMap.put(current1,null);
            current1 = current1.next;
        }
        while(current2 != null){
            if(hashMap.containsKey(current2)){
                return current2;
            }
            current2 = current2.next;
        }
        return null;
    }
}