链表逆序

链表逆序就是把一个链表按照原来的链接顺序逆序实现（也就是将头变成尾，尾变成头）。

编程思路：其实最关键的是先通过原来的链接顺序找到下个节点，然后再把前个节点反序。

链表的头节点如下：

struct ListNode{void*       m_nKey;ListNode* m_pNext;}; 

常规实现：

ListNode* ReverseIteratively(ListNode* pHead){ListNode* pReversedHead = NULL;ListNode* pNode = pHead;ListNode* pPrev = NULL;while(pNode != NULL){// get the next node, and save it at pNextListNode* pNext = pNode->m_pNext;   // if the next node is null, the currect is the end of original  // list, and it's the head of the reversed list    if(pNext == NULL)     pReversedHead = pNode;    // reverse the linkage between nodes    pNode->m_pNext = pPrev;   // move forward on the the list    pPrev = pNode;  pNode = pNext;   }}

递归实现（不需要临时节点）：

ListNode* reverse_list( ListNode* head)       //逆序{ListNode* new_head=head;if(head==NULL || head->next==NULL)return head;new_head = reverse_list(head->next);head->next->next=head;head->next=NULL; //防止链表成为一个环，这是最关键的。return new_head; }