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

    ListNode(int val) {
        this.val = val;
    }
}*/
//时间复杂度:O(m+n)  空间复杂度O(1)
import java.util.*;
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        ListNode l1=pHead1;
        ListNode l2 = pHead2;
        while(l1!=l2){
            l1=(l1==null)?pHead2:l1.next;
            l2=(l2==null)?pHead1:l2.next;
        }
        return l1;
    }
}