//Test is T74_75.cpp		#include <stdio.h>		#include <iostream.h>		class List;							//List類的前視聲明		class ListNode {						//結點類定義		friend class List;		friend ostream & operator << ( ostream&, List & );						//聲明List類為友元類		public:		   //ListNode() { data = 0; link = NULL; );		   ListNode( int x, ListNode * p ) { data = x; link = p; }		private:		   int data;							//數據元素域		   ListNode *link;						//鏈指針域		};		class List {							//List類定義		friend ostream & operator << ( ostream&, List & );						//聲明List類為友元類		public:		   List(): first( NULL ) {};		   //鏈表公共操作		   //………		   int Insert ( const int x, const int i );		   int Remove ( int i );		private:		   ListNode *first, *last;					//指向鏈表表頭的指針		};		#include <iostream.h>		int List::Insert ( const int x, const int i ) {		//將新元素x插入到第i結點之前。i是結點號，從0開始。		   ListNode *p = first;  int k = 0;		   while ( p != NULL && k< i-1 ) { p = p->link;  k++; }		//循鏈找第i-1個結點		   if ( p == NULL && first != NULL ) {				//非空表而且鏈短，找不到第i-1個結點			 cout << "Invalid position for Insertation!\n";  return 0;	//終止插入, 函數返回0		   }		   ListNode *newnode= new ListNode( x, NULL );				//建立一個newnode指示的新結點, 數據為x		   if ( first == NULL || i == 0 ) {					//插入空表或非空表第一個結點之前			  newnode->link = first;						//新結點成為第一個結點			  if ( first == NULL ) last = newnode;				//原為空表時，表尾指針指向這個新結點			  first = newnode;		   }		   else {									//插入在鏈表的中間或尾部			  newnode->link = p->link;			  if ( p->link == NULL ) last = newnode;			  p->link = newnode;		}		   return 1;									//正常插入，函數返回1		}		int List::Remove ( int i ) {		//將鏈表中的第i個元素刪去, 通過函數返回該元素。若i不合理, 則返回NULL。		   if ( i < 0 ) { cout << "Invalid position for Deletion!\n";  return 0;}	//不能刪除, 函數返回0		   ListNode *p = first, *q;  int k = 0;		   while ( p != NULL && k< i-1 ) { p = p->link; k++; }		//循鏈找第i-1個結點		   if ( p == NULL || p->link == NULL ) {							//空表或者鏈短，找不到第i-1個結點			  cout << "Invalid position for Deletion!\n";  return 0;	//不能刪除, 函數返回0		   }		   if ( i == 0 ) {	q = first;  p = first = first->link; } 		//刪第一個結點時，重新拉鏈		   else { q = p->link;  p->link = q->link; }			//刪中間一個結點或尾結點時		   if ( q == last ) last = p;						//刪表尾結點時, 表尾指針修改		   k = q->data;  delete q;  return k;					//取出被刪結點中的數據值		}		ostream & operator << ( ostream& os , List & onelist) {		    ListNode * p = onelist.first;		    if ( p == NULL ) os << "It is empty";		    else while ( p != NULL ) {			     os << p->data << " " ;			     p = p->link;			 }		    return os;		}