[LeetCode]141. Linked List Cycle

141. Linked List Cycle
Given a linked list, determine if it has a cycle in it.

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

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/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    bool hasCycle(ListNode *head) {        ListNode* fast = head;        ListNode* slow = head;        while(fast && fast->next){            fast = fast->next->next;            slow = slow->next;            if(fast == slow)                return true;        }        return false;    }};