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) {
    }
};
*/
#include <map>

class Solution {
public:
    ListNode* EntryNodeOfLoop(ListNode* pHead) {
        std::map<ListNode*, size_t> mem;
        for(auto cur = pHead; cur; cur = cur->next) {
            if(mem.count(cur)) return cur;
            mem.emplace(cur, 1);
        }
        return nullptr;
    }
};