28.输入两个链表，找出它们的第一个公共结点。

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题目描述

输入两个链表，找出它们的第一个公共结点。

解题思路：先求两个链表的长度，决定让哪一个链表先走，然后在判断节点是否相等；

/*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;        }        int count1 = 0;        ListNode p1 = pHead1;        while(p1!=null){            p1 = p1.next;            count1++;        }        int count2 = 0;        ListNode p2 = pHead2;        while(p2!=null){            p2 = p2.next;            count2++;        }        int flag = count1 - count2;        if(flag>0){            while(flag>0){                pHead1 = pHead1.next;                flag--;            }            while(pHead1!=pHead2){                pHead1 = pHead1.next;                pHead2 = pHead2.next;            }            return pHead1;        }        if(flag<=0){            while(flag<0){                pHead2 = pHead2.next;                flag++;            }            while(pHead1!=pHead2){                pHead2 = pHead2.next;                pHead1 = pHead1.next;            }            return pHead2;        }        return null;    }}

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