题目链接：两个链表的第一个公共节点

import java.util.*;
/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindFirstCommonNode(ListNode head1, ListNode head2) {
        ListNode p = head1, q = head2;
        
        while(p != q)
        {
            if(p != null) p = p.next;
            else p = head2;
            if(q != null) q = q.next;
            else q = head1;
        }

        return q;
    }
}