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) {
        if(pHead->next == nullptr) return nullptr;
        ListNode* slow = pHead->next;
        ListNode* fast = pHead->next->next;
        while((fast != nullptr && fast->next != nullptr) && fast != slow){
            fast = fast->next->next;
            slow = slow ->next;
        };
        if(fast == nullptr || fast->next == nullptr) return nullptr;
        ListNode* curr = pHead;
        while(curr != slow){
            curr = curr->next;
            slow = slow ->next;
        }
        return curr;

    }
};