PTA 实现链式表的操作集

本题要求实现链式表的操作集。

函数接口定义：
Position Find( List L, ElementType X );
List Insert( List L, ElementType X, Position P );
List 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：

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

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

List Delete( List L, Position P )：将位置P的元素删除并返回链表的表头。若参数P指向非法位置，则打印“Wrong Position for Deletion”并返回ERROR。

裁判测试程序样例：
#include <stdio.h>
#include <stdlib.h>

#define ERROR NULL
typedef int ElementType;
typedef struct LNode *PtrToLNode;
struct LNode {
ElementType Data;
PtrToLNode Next;
};
typedef PtrToLNode Position;
typedef PtrToLNode List;

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

int main()
{
List L;
ElementType X;
Position P, tmp;
int N;

L = NULL;
scanf("%d", &N);
while ( N-- ) {
    scanf("%d", &X);
    L = Insert(L, X, L);
    if ( L==ERROR ) 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 {
        L = Delete(L, P);
        printf("%d is found and deleted.\n", X);
        if ( L==ERROR )
            printf("Wrong Answer or Empty List.\n");
    }
}
L = Insert(L, X, NULL);
if ( L==ERROR ) printf("Wrong Answer\n");
else
    printf("%d is inserted as the last element.\n", X);
P = (Position)malloc(sizeof(struct LNode));
tmp = Insert(L, X, P);
if ( tmp!=ERROR ) printf("Wrong Answer\n");
tmp = Delete(L, P);
if ( tmp!=ERROR ) printf("Wrong Answer\n");
for ( P=L; 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

Position Find( List L, ElementType X )
{
	while(L){
		if(L -> Data == X){
			return L;
		}
		L = L -> Next;
	}
	return ERROR;
}
List Insert( List L, ElementType X, Position P )//只考虑头结点和中间结点两种情况 
{
	List p = (List)malloc(sizeof(List));
	p -> Next = NULL;//初始化 不然后面乱指 不安全 
	p -> Data = X;
	List Head = L;//返回头指针 
	if(P == L){
		p -> Next = L;
		return p;
	}
	while(L){
		if(L -> Next == P){
			p -> Next = L -> Next;
			L -> Next = p;
			return Head;
		}
		L = L -> Next;
	}
	printf("Wrong Position for Insertion\n");
	return ERROR;
}

List Delete( List L, Position P )
{
	List Head = L;
	if(P == L){
		L = L -> Next;
		return L;
	}
	while(L){
		if(L -> Next == P){
			L -> Next = P -> Next;
		    return Head;
		}
		L = L -> Next;
	}
	printf("Wrong Position for Deletion\n");
	return ERROR;
}