[LeetCode]Linked List Cycle

题目描述：

Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

解题方案：

使用快慢指针，如果有环，快指针肯定会追上慢指针。下面是该题的代码：

class Solution {
public:
    bool hasCycle(ListNode *head) {
        struct ListNode *slow = head;
        struct ListNode *fast = head;
        
        while (fast != NULL && fast->next != NULL) {
            slow = slow->next;
            fast = fast->next->next;
            
            if (slow == fast) {
                return true;
            }
        }
        return false;
    }
};