题解 | #判断链表中是否有环#

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool hasCycle(ListNode *head) {
        //cout << head->next->val;
        //if(head == nullptr)    return false;
        ListNode * fast_ptr = head;
        ListNode * slow_ptr = head;
        while(fast_ptr != nullptr && fast_ptr->next != nullptr){
            slow_ptr = slow_ptr->next;
            fast_ptr = fast_ptr->next->next;
            //判断两个节点是否相同，不直接判断值的原因是可能是空指针
            if(slow_ptr == fast_ptr)
                return true;
        }
        return false;
    }
};