C++ 代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    unordered_map<ListNode*,int> pos;
    ListNode *entryNodeOfLoop(ListNode *head) {
        for(ListNode*p=head;p;p=p->next){
            if(pos[p]==1){
                return p;
            }else{
                pos[p]++;
            }
        }
        return NULL;
    }
};