Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
/**
* 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* p1 = head, *p2 = head;
while(true){
if(NULL == p2 || NULL == p1) return false;
p1 = p1->next;
p2 = p2->next;
if(NULL == p2) return false;
p2 = p2->next;
if(p2 == p1) return true;
}
}
};
