题解 | #判断链表中是否有环#

/**
 * struct ListNode {
 *    int val;
 *    struct ListNode *next;
 * };
 */

/**
 * 
 * @param head ListNode类 
 * @return bool布尔型
 */
bool hasCycle(struct ListNode* head ) {
    // write code here
    if (head==NULL||head->next==NULL||head->next->next==NULL) return false;
    struct ListNode *slow = head, *fast = head;
    while (fast && fast->next) {
         slow = slow->next;
         fast = fast->next->next;
         if (slow == fast) return true;
        }
     return false;
}