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

    struct ListNode* fast = head;
    struct ListNode* slow = head;

    if(head == NULL || head -> next == NULL || head -> next -> next == NULL){
        return false;
    }

    do{
        if (fast == NULL || fast->next == NULL) {
        return false;
    }
        fast = fast -> next -> next;
        slow = slow -> next;
    }while(fast != slow && fast != NULL && slow != NULL);

    if(fast == slow){
        return true;
    }else{
        return false;
    }
}