题解 | #判断链表中是否有环#

#include <stdbool.h>
/**
 * 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)
    {
        return false;
    }
    struct ListNode* slow = head ;
    struct ListNode* fast = head;
    while (fast != NULL && fast->next != NULL) {
        slow = slow->next;
        fast = fast->next;
        if(fast != NULL)
        {
            fast = fast->next;
        }
        if (slow == fast) {
            return true;
        }
    }
    return false;
}
按照之前的写法应该是直接slow = head;fast = head->next;然后在while循环中各指向下一个，但是这样编译不过，所有只能将fast和slow同时初始为head，然后再slow移动一步，fast移动两步后再进行比较