LeetCode 环形链表 C语言

• 思路
  之前学习过快慢指针法，可用于判断循环或求中位数，于是用在这里
  快指针每次走两步，慢指针每次走一步，若不存在环，则不会相遇，若存在必定会相遇
• 贴上代码，此版本执行时间较短

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
bool hasCycle(struct ListNode *head) {
    if(head == NULL || head->next == NULL)
        return false;
    struct ListNode *slow = head;
    struct ListNode *fast = head;
    fast = fast->next->next;
    slow = slow->next;
    while(1){
        if(fast == NULL || fast->next == NULL)
            return false;
        else if(fast == slow || fast->next == slow)
            return true;
        else{
            fast = fast->next->next;
            slow = slow->next;
        }
    }
}