public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
         if(pHead1 == null || pHead2 == null){
             return null;
         }
        ListNode p1 = pHead1;
        ListNode p2 = pHead2;
        //有环 无环 链表题目中说了是无环 先到终点为null的节点从头来,后到的就慢了几个节点,最终会逐渐缩小
        while(p1 != p2  ){
            p1 = p1 != null ?p1.next: pHead1;
            p2 = p2 !=  null ?p2.next :pHead2;
        }
        return p1;
        
    }
}