单链表逆序的几种方法

  struct ListNode {
      int val;
      ListNode *next;
      ListNode(int x) : val(x), next(NULL) {}
  };

ListNode* reverseList(ListNode* head) {
        ListNode *newNode = new ListNode(0);//新链表头结点
        ListNode *tmp;//指向原先链表的第一个结点
        newNode->next = head;
        ListNode *cur = head;
        while(cur && cur->next)
        {
        tmp = newNode->next;//保存后续结点
        newNode->next = cur->next;//将原先链表的第一个结点放到新链表中                         
        cur->next = cur->next->next;//从原先链表中摘除这个结点
        newNode->next->next = tmp;//恢复新链表中后续结点的指针
        }
        return newNode;
        
    }    

ListNode* reverseList(ListNode* head) {
       ListNode *tmp = NULL;
       ListNode *cur = NULL;
       if(!head) return NULL;
       cur = head->next;
       while(cur)
       {
              tmp = cur->next;
              cur->next  = tmp->next;
              tmp->next = head->next;
              head->next = tmp;
       }  
        return head;
    }

ListNode* reverseList(ListNode* head) {
        ListNode *cur = head;
        ListNode *tmp, *prev = NULL;
        while (cur)
        {
            tmp = cur->next;
            cur->next = prev;
            prev = cur;
            cur = tmp;
        }
        return prev;
    }