给定头,链接列表的头,确定链接列表是否包含循环.如果列表中有一些节点可以通过连续跟踪下一个指针再次访问,则链接列表中存在循环.内部,pos用于表示尾巴下一个指针连接的节点的索引.请注意pos不是作为参数传递的.如果链接列表中存在循环,返回true.否则返回false.
One approach to detect the cycle in a linked list is Floyd's cycle-finding algorithm, also known as hare and tortoise algorithm. In this approach, two pointers, a slow pointer and a fast pointer, traverse the linked list. If the linked list contains a cycle, eventually, the fast pointer will catch up with the slow pointer.

Here's the code for implementing Floyd's algorithm:

```
bool hasCycle(ListNode *head) {
    if (head == nullptr || head->next == nullptr) {
        return false;
    }
    ListNode* slow = head;
    ListNode* fast = head->next;
    while (slow != fast) {
        if (fast == nullptr || fast->next == nullptr) {
            return false;
        }
        slow = slow->next;
        fast = fast->next->next;
    }
    return true;
}
```

The time complexity of this algorithm is O(n) and the space complexity is O(1), where n is the number of nodes in the linked list.