面试题03：反转链表

题目：输入一个链表的头结点，反转该链表，并返回反转后链表的头结点。链表结点定义如下：

struct List{      int       value;      ListNode* next;};

1、循环方法

//反转链表List* ReverseList(List* pHead){    List* pNode = pHead;    List* pPre = NULL;    List* pReverseHead = pNode;    while (pNode != NULL){        if (pNode->next == NULL){            pReverseHead = pNode;        }        List* pNext = pNode->next;        pNode->next = pPre;        pPre = pNode;        pNode = pNext;    }    return pReverseHead;}

2、递归方法

void reverse(List*& p) {    if (!p) return;    List* rest = p->next;    if (!rest) return;    reverse(rest);    p->next->next = p;    p->next = NULL;    p = rest;}