題目描述
一個(gè)鏈表中包含環(huán)，請(qǐng)找出該鏈表的環(huán)的入口結(jié)點(diǎn)

class Solution {
public:
    ListNode* EntryNodeOfLoop(ListNode* pHead)
    {
        if(pHead == NULL)
            return NULL;
        ListNode* p1 = pHead;
        ListNode* p2 = pHead;
        while(p2&&p2->next)
        {
            p1 = p1->next;
            p2 = p2->next->next;
            if(p1==p2)
                break;
        }
        if(p2==NULL||p2->next==NULL)
            return NULL;
        p1 = pHead;
        while(p1!=p2)
        {
            p1 = p1->next;
            p2 = p2->next;
        }
        return p1;
    }
};