反转链表

/*struct ListNode {    int val;    struct ListNode *next;    ListNode(int x) :            val(x), next(NULL) {    }};*/class Solution {public:    ListNode* ReverseList(ListNode* pHead) {        if (pHead == NULL)        {            return NULL;        }        vector<ListNode* > v;        ListNode* temp = pHead;        while (temp != NULL)        {            v.push_back(temp);            temp = temp->next;        }        vector<ListNode* >::iterator it;        for (it = v.end()-1; it != v.begin(); it--)        {            (*it)->next = *(it-1);        }        (*it)->next = NULL;        it = v.end()-1;        return *it;    }};