文章目录

• 思路
• 代码

思路

one_step指针每轮循环向前走一步
double_step指针每轮循环向前走两步
double_step指针速度快于double_step指针
double_step指针判断前面两步是否为null，若为空则说明无环形
再判断前面两步是否与one_step指针相逢，若相逢说明有环形

代码

bool hasCycle(struct ListNode *head) {
    if(head==NULL) return false;
    struct ListNode *one_step=head,*double_step=head->next;
    bool ret = false;
    while(1){
        if(double_step==NULL || double_step->next==NULL) break;
        if(double_step==one_step || double_step->next==one_step){ ret=true;break;}

        one_step = one_step->next;
        double_step = double_step->next->next;
    }
    return ret;
}