题解 | #两个链表的第一个公共结点#

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

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {

        if(pHead1==null||pHead2==null){
            return null;
        }

        ListNode p1 = pHead1;
        ListNode p2 = pHead2;

        while(p2.next!=null){
            p2 = p2.next;
        }
        p2.next = pHead2;



        ListNode t1 = pHead1;
        ListNode t2 = pHead1;
        while(t1!=null&&t1.next!=null){

            t1 = t1.next.next;
            t2 = t2.next;

            if(t1==t2){
                ListNode target = pHead1;
                while(t2!=target){
                    t2 = t2.next;
                    target = target.next;
                }
                p2.next = null;
                return target;
            }
            
        }

        return null;

        
 
    }
}

思路：将其中一个链表的尾节点连接头节点，形成一个环。那么问题就变成了寻找环的入口