链表倒置，这个还是考验仔细程度，第一遍还没做对 —— 剑指Offer

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if (pHead == NULL || pHead->next == NULL) return pHead;
        
        ListNode *pFirst = NULL;
        ListNode *pSecond = pHead;
        // 开始下面两行倒了，有bug
        ListNode *pThird = pSecond->next;
        pSecond->next = pFirst;
        
        while (pThird != NULL) {
            pFirst = pSecond;
            pSecond = pThird;
            pThird = pThird->next;
            pSecond->next = pFirst;
        }
        
        return pSecond;
    }
};