Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
Follow up:
Can you solve it without using extra space
之前的the beginning of the loop也有介绍
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *detectCycle(ListNode *head) {
ListNode *p = head, *q = head;
while (q && q->next){
p = p->next;
q = q->next->next;
if (q == p)
break;
}
if(q && q->next){
q = head;
while (p != q){
p = p->next;
q = q->next;
}
return p;
}
return NULL;
}
};