141.环形链表

🚌双指针实现

class Solution {
public:
    bool hasCycle(ListNode *head) {
        ListNode* slow_ptr = head, 
            *quick_ptr = head;
        if(!head)
            return false;
        while(1) {
            quick_ptr = quick_ptr->next;
            if(!quick_ptr)
                return false;
            else if(quick_ptr == slow_ptr)
                return true;
            quick_ptr = quick_ptr->next;
            if(!quick_ptr)
                return false;
            else if(quick_ptr == slow_ptr)
                return true;
            slow_ptr = slow_ptr->next;
        }
        return true;
    }
};

Accepted

17/17 cases passed (12 ms)

Your runtime beats 83.52 % of cpp submissions

Your memory usage beats 19.93 % of cpp submissions (10 MB)