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1:

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

输出样例1:

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 

c代码

Position Find( List L, ElementType X ) {  //按值查找
    List p = L;   
    for (p = L; p ; p = p -> Next)     //从头结点开始遍历，找到就返回当前位置
        if(p -> Data == X)  return p;
    return ERROR;   //没找到
}

List Insert( List L, ElementType X, Position P ) {    //插入
    List p = (List)malloc(sizeof (struct LNode));    
    p -> Data = X;
    p -> Next = NULL;
    if(P == L) {     //插在L前
        p -> Next = L;    //新结点q的后继改为L
        return p;
    }else {        //插在中间或者最后
        List q;
        for (q = L; q ; q = q -> Next) {    //遍历
            if(q -> Next == P) {      //当前结点是要插入结点的前一个
                p -> Next = P;        //新结点的后继改为P
                q -> Next = p;        //当前节点的后继改为新节点
                return L;
            }
        }
    }
    puts("Wrong Position for Insertion");   //其他情况
    return ERROR;
}

List Delete( List L, Position P ) {
    if(L == P) {      //删除头节点
        L = L -> Next;     //头节点指向下一个结点
        return L;
    }
    
    List p, q;
    for (p = L, q = L; p ; p = p -> Next) {  //删除中间最后的
        if(p == P) {
            q -> Next = p -> Next;   //上一个结点的后继改为当前结点的后继
            free(P);     //释放P结点
            return L;
        } else q = p;      //q记录当前节点的上一个节点
    }
    
    puts("Wrong Position for Deletion");    //其他情况
    return ERROR; 
}