单链表的反转 c++

#include<iostream>

#include<stdexcept>

using namespace std;

const int N=10;

typedef struct node

{ int key;

  struct node*next;

} NODE;

// INSERT A ELEMENT INTO A LINKLIST

bool insert(NODE*p,int position,int key)//insert an elemnt which will be the position-th element of the linklist;if fail to insert an element return false otherwise return true;position:1,2,3~~~~~~~

{  if(NULL==p)

    {cout<<"the linklist do not exist!";

    return false;

    }

   else

   {

   int i=0;

   NODE*p_find=p;//we will insert a new node following the node which is pointed by f_find

   NODE*p_new=NULL;

   while((i<position-1)&&p_find->next!=NULL)

         { p_find=p_find->next;

           ++i;

         }

   if(i!=position-1)// indicate that fail to find the position!

     return false;

   else

   {   try

         { p_new=new NODE;

         }       

      catch(bad_alloc)

        { cout<<"There is not enough memory to be allocated"<<endl;

          return false;

        }

      p_new->key=key;

      p_new->next=p_find->next;

      p_find->next=p_new;

      return true;

   }

   

   }

}

NODE*create_empty_linklist() //create a new empty linklist

{  NODE*p=NULL;

   try{p=new NODE;

      }

   catch(bad_alloc)

   { cout<<"there is no enough memory to be allocated ";

     return NULL;

   }

   p->next=NULL;

   return p;

}

void free_all_linklist(NODE*p)// free all the node in a linklist

{  NODE*pp=NULL;

   while(p!=NULL)

    { pp=p->next;

      delete p;

      p=pp;

    }

}

/************反转链表的程序************************/

/************反转链表的程序************************/

void reverse_linklist(NODE*p)// reverse a linklist; example:from  head_node->1->2->3->4   to  head_node->4->3->2->1

{  if(NULL!=p)

     {  NODE*p1=NULL,// 指向要反转的节点的前一个node，初始化必须为NULL；因为第一个节点的next域应该为NULL

        *p2=p->next,//要反转的node，p2被初始化为链表的第一个节点

        *p_save=NULL;//保存指向要反转的node的下一个节点的指针，因为反转后链表断裂，若不保存无法继续迭代

        while(NULL!=p2)

        { p_save=p2->next;

          p2->next=p1;//反转指针

          p1=p2;//移动p1

          p2=p_save;

        }

         p->next=p1;//头节点指向原来的尾元素

    }

    else

    throw runtime_error("the linklist needed to be reversed is NULL!");

}

/************反转链表的程序************************/

/************反转链表的程序************************/

void iter_print(const NODE*head)//打印链表

{ const NODE*p=head->next;

  while(p!=NULL)

       {cout<<p->key<<"  ";

        p=p->next;

       }

       cout<<endl;

}

int main(void)

{  int a
={1,2,3,4,5,5,5,6,7,7},

       i=0;

   NODE*head=create_empty_linklist();

   for(;i<N;++i)

      insert(head,1,a[i]);

      iter_print(head);

      reverse_linklist(head);

      iter_print(head);

      free_all_linklist(head);

      return 0;

      

}