题解 | #链表中环的入口结点#

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* EntryNodeOfLoop(ListNode* pHead) {
        unordered_set<ListNode *> my;
        while(pHead ){
           //1.方法1
            if(my.find(pHead)  != my.end())
            return pHead;
            my.insert(pHead);
            pHead = pHead->next;
		  //2.方法2，两者都是用hash的原理实现
             // if(my.count(pHead)) return pHead;
            //my.insert(pHead);
            // pHead = pHead->next;
        }
        return nullptr;
    }
};