【LeetCode】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?

Hide Tags: Linked List Two Pointers

Hide Similar Problems: (M) Linked List Cycle II

Solution:

/**
 * 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) {
        if(!head || !head->next)return false;
        ListNode *faster = head;
        ListNode *slower = head;
        while(faster->next && faster->next->next){
            faster=faster->next->next;
            slower=slower->next;
            if(faster==slower)
                return true;
        }
        return false;
    }
};