找出两个链表的第一个公共结点

 public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        ListNode p1=pHead1;
        ListNode p2=pHead2;
        while(p1!=p2){
            p1= p1==null?pHead2:p1.next;
            p2= p2==null?pHead1:p2.next;
        }
        return p1;
    }

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