0141-linked-list-cycle.c

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