给一个链表,若其中包含环,请找出该链表的环的入口结点,否则,输出null。
struct ListNode {
int val;
struct ListNode *next;
ListNode(int x) :
val(x), next(NULL) {
}
};
class Solution {
public:
ListNode* hasCircle(ListNode* phead)
{
ListNode* slow=phead;
ListNode* fast=phead;
while(fast!=NULL)
{
slow=slow->next;
fast=fast->next;
if(fast==NULL) return NULL;
fast=fast->next;
if(fast==slow) break;
}
return slow;
}
ListNode* EntryNodeOfLoop(ListNode* pHead)
{
ListNode *p=hasCircle(pHead);
if(p==NULL) return NULL;
ListNode *ph=pHead;
while(p!=ph){
p=p->next;
ph=ph->next;
}
return p;
}
};