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

结尾无空行

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 

结尾无空行

我的代码：

Position Find( List L, ElementType X ) {
	List p;
	for (p = L; p != NULL; p = p->Next) {
		if (p->Data == X)
			return p;
	}
	return ERROR;
}

List Insert( List L, ElementType X, Position P ) {
	List p = (List)malloc(sizeof(struct LNode));
	p->Data = X;
	p->Next = NULL;
	if (P == L) {
		p->Next = L;
		return p;
	}
    //链表为空或位置在头结点的情况
	List temp = L;
	while (temp) {
		if (temp->Next == P) {
			p->Next = temp->Next;
			temp->Next = p;
			return L;
		}
		temp = temp->Next;
	}
    //链表存在且P存在的情况
	printf("Wrong Position for Insertion\n");
	return ERROR;
    //最后为链表非空且P是非法位置的情况
}

List Delete( List L, Position P ) {
	List temp, find = L;
	if (P == L) {
		L = L->Next;
		free(P);
		return L;
	}
	while (find) {
		if (find->Next == P) {
			find->Next = P->Next;
			free(P);
			return L;
		}
		find = find->Next;
	}
	printf("Wrong Position for Deletion\n");
	return ERROR;
}
//删除操作的情况分类跟插入操作差不多