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
    //解题思路 下标标记法 or 快慢指针 本用快慢指针
    struct ListNode* slow = head, *fast = head;
    if(slow == NULL || slow->next == NULL) {
        return false;
    }
    while(fast->next != NULL) {
        fast = fast->next;
        if(fast->next != NULL) {
            fast = fast->next;
            slow = slow->next;
            if(fast == slow)
                return true;
        }
    }
    return false;
}