思路：
把一个链表结点存到hashmap里，遍历另一个链表对hashmap对象使用containskey方法判断即可
实现：
/*
public class ListNode {
int val;
ListNode next = null;
ListNode(int val) {
this.val = val;
}
}*/
import java.util.HashMap;
public class Solution {
public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
ListNode cur1 = pHead1;
ListNode cur2 = pHead2;
HashMap<ListNode,Integer> map = new HashMap<>();
while(cur1 != null){
map.put(cur1,null);
cur1 = cur1.next;
}
while(cur2 != null){
if(map.containsKey(cur2)){
return cur2;
}
cur2 = cur2.next;
}
return null;
}
}