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 { // 快慢指针法
public:
    bool hasCycle(ListNode *head) {
        if(!head)
            return false;
        ListNode* slow = head;
        ListNode* fast = head;
        while(fast && fast->next){
            slow = slow->next;
            fast = fast->next->next;
            if(slow == fast)
                return true;
        }
        return false;
    }
};

class Solution { // 删除节点法
public:
    bool hasCycle(ListNode *head) {
        if(!head)
            return false;
        ListNode* post = head->next;
        while(post){
            head->next = head;
            head = post;
            post = post->next;
            if(head == head->next)
                return true;
        }
        return false;

    }
};