剑指offer反转链表

way1：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

/*struct ListNode {     int val;     struct ListNode *next;     ListNode(int x) :             val(x), next(NULL) {     } };*/ class Solution { public:     ListNode* ReverseList(ListNode* pHead) {         ListNode *p1,*p2,*p3;         if(NULL!=pHead)             p1=pHead;         else             return NULL;         if(NULL!=p1->next)             p2=p1->next;         else             return p1;         if(NULL!=p2->next)         {             p3=p2->next;             p1->next=NULL;         }         else         {             p1->next=NULL;             p2->next=p1;             return p2;         }                    while(NULL!=p3->next)         {             p2->next=p1;             p1=p2;             p2=p3;             p3=p3->next;                                           }         p3->next=p2;         p2->next=p1;         return p3;     } };

way2：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

/*struct ListNode {     int val;     struct ListNode *next;     ListNode(int x) :             val(x), next(NULL) {     } };*/ class Solution { public:     ListNode* ReverseList(ListNode* pHead) {         ListNode* p1=NULL;         ListNode* p2=pHead;         ListNode* p3=NULL;         ListNode* newHead=NULL;         while(NULL!=p2)         {             p3=p2->next;             if(NULL==p3)                 newHead=p2;             p2->next=p1;             p1=p2;             p2=p3;         }         return newHead;     } };