141

环形链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
bool hasCycle(struct ListNode *head) {
    struct ListNode *p = head, *q = head;
    if(p == NULL) return false;
    do{
        p = p->next;
        q = q->next;
        if(q == NULL || q->next == NULL) return false;
        q = q->next;
    }while(p != q);
    return true;
}