双指针 和力扣 160 相同 原理：https://leetcode-cn.com/problems/intersection-of-two-linked-lists/solution/intersection-of-two-linked-lists-shuang-zhi-zhen-l/

public class Solution {
    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;
    }
}