带头结点的链式表操作集 （20 分)

本题要求实现带头结点的链式表操作集。

函数接口定义：

List MakeEmpty(); 
Position Find( List L, ElementType X );
bool Insert( List L, ElementType X, Position P );
bool Delete( List L, Position P );

其中List结构定义如下：

typedef struct LNode *PtrToLNode;
struct LNode {
    ElementType Data;
    PtrToLNode Next;
};
typedef PtrToLNode Position;
typedef PtrToLNode List;

各个操作函数的定义为：

List MakeEmpty()：创建并返回一个空的线性表；

Position Find( List L, ElementType X )：返回线性表中X的位置。若找不到则返回ERROR；

bool Insert( List L, ElementType X, Position P )：将X插入在位置P指向的结点之前，返回true。如果参数P指向非法位置，则打印“Wrong Position for Insertion”，返回false；

bool Delete( List L, Position P )：将位置P的元素删除并返回true。若参数P指向非法位置，则打印“Wrong Position for Deletion”并返回false。

裁判测试程序样例：

#include <stdio.h>
#include <stdlib.h>

#define ERROR NULL
typedef enum {false, true} bool;
typedef int ElementType;
typedef struct LNode *PtrToLNode;
struct LNode {
    ElementType Data;
    PtrToLNode Next;
};
typedef PtrToLNode Position;
typedef PtrToLNode List;

List MakeEmpty(); 
Position Find( List L, ElementType X );
bool Insert( List L, ElementType X, Position P );
bool Delete( List L, Position P );

int main()
{
    List L;
    ElementType X;
    Position P;
    int N;
    bool flag;

    L = MakeEmpty();
    scanf("%d", &N);
    while ( N-- ) {
        scanf("%d", &X);
        flag = Insert(L, X, L->Next);
        if ( flag==false ) printf("Wrong Answer\n");
    }
    scanf("%d", &N);
    while ( N-- ) {
        scanf("%d", &X);
        P = Find(L, X);
        if ( P == ERROR )
            printf("Finding Error: %d is not in.\n", X);
        else {
            flag = Delete(L, P);
            printf("%d is found and deleted.\n", X);
            if ( flag==false )
                printf("Wrong Answer.\n");
        }
    }
    flag = Insert(L, X, NULL);
    if ( flag==false ) printf("Wrong Answer\n");
    else
        printf("%d is inserted as the last element.\n", X);
    P = (Position)malloc(sizeof(struct LNode));
    flag = Insert(L, X, P);
    if ( flag==true ) printf("Wrong Answer\n");
    flag = Delete(L, P);
    if ( flag==true ) printf("Wrong Answer\n");
    for ( P=L->Next; P; P = P->Next ) printf("%d ", P->Data);
    return 0;
}
/* 你的代码将被嵌在这里 */

输入样例：

6
12 2 4 87 10 2
4
2 12 87 5

输出样例：

2 is found and deleted.
12 is found and deleted.
87 is found and deleted.
Finding Error: 5 is not in.
5 is inserted as the last element.
Wrong Position for Insertion
Wrong Position for Deletion
10 4 2 5 
List MakeEmpty(){
	List L;
	L=(List)malloc(sizeof(struct LNode));
	L->Next=NULL;
	return L;
}
Position Find( List L, ElementType X ){
	L=L->Next;
	while(L!=NULL){
		if(L->Data==X)
		return L;
		L=L->Next; 
	}
	return ERROR;
}
bool Insert( List L, ElementType X, Position P ){
	List pre=L;
	L=L->Next;
	while(L!=NULL){
		if(L==P){
			List pt=(List)malloc(sizeof(struct LNode));
			pt->Data=X;
			pt->Next=pre->Next;
			pre->Next=pt;
			return true;
		}
		pre=L;
		L=L->Next;
	}
	if(P==NULL){
		List pt=(List)malloc(sizeof(struct LNode));
		pt->Data=X;
		pt->Next=NULL;
		pre->Next=pt;
		return true;
	}
	printf("Wrong Position for Insertion\n");
	return false;
}
bool Delete( List L, Position P ){
	List pre=L;
	L=L->Next;
	while(L!=NULL){
		if(L==P){
			pre->Next=L->Next;
			return true;
		}
		pre=L;
		L=L->Next;
	}
	printf("Wrong Position for Deletion\n");
	return false;
}