题解 | #链表中环的入口结点#

class Solution {
public:
    ListNode* EntryNodeOfLoop(ListNode* pHead) {
        ListNode* node=pHead;
        unordered_set<ListNode*>S;
        while(node!=NULL)
        {
            if(S.end()!=S.find(node))
            {
                return node;
            }
            else
            {
                S.insert(node);
            }
            node=node->next;
        }
        
        return NULL;
    }
};