翻转链表

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
      if(pHead==nullptr||pHead->next==nullptr)  return pHead;

     ListNode *p=pHead->next;
     ListNode *q=p->next;
      pHead->next=nullptr;
       while(p)
       {
          p->next=pHead;
           pHead=p;
           p=q;
           if(q) q=q->next;

        }
        return pHead;
    }
};