要求實現帶頭結點的鏈式表操作集。

函式介面定義：

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結構定義如下：

typedef struct LNode *PtrToLNode;
struct LNode {
ElementType Data;
PtrToLNode Next;
};
typedef PtrToLNode Position;
typedef PtrToLNode List;
各個操作函式的定義為：

List MakeEmpty()：建立並返回一個空的線性表；

Position Find( List L, ElementType X )：返回線性表中X的位置。若找不到則返回ERROR；

bool Insert( List L, ElementType X, Position P )：將X插入在位置P指向的結點之前，返回true。如果引數P指向非法位置，則列印“Wrong Position for Insertion”，返回false；

bool Delete( List L, Position P )：將位置P的元素刪除並返回true。若引數P指向非法位置，則列印“Wrong Position for Deletion”並返回false。

裁判測試程式樣例：

#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;
}
/* 你的程式碼將被嵌在這裡 */

輸入樣例：

6
12 2 4 87 10 2
4
2 12 87 5
輸出樣例：

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

【答案】：

List MakeEmpty(){
    List A;
    A=(List)malloc(sizeof(struct LNode));
    A->Next=NULL;
    return A;
}
Position Find(List L,ElementType X){
    Position p;
    p=L;
    for(;p->Data!=X&&p;p=p->Next);
    if(p==NULL)return ERROR;
    else return p;
}

bool Insert(List L,ElementType X,Position P){
    Position pre,r;

    for(pre=L;pre&&pre->Next!=P;pre=pre->Next);
    if(pre==NULL){
        printf("Wrong Position for Insertion");
        return false;
    }
    else{
        r=(Position)malloc(sizeof(struct LNode));
        r->Data=X;
        r->Next=P;
        pre->Next=r;
        return true;
    }
}
bool Delete(List L,Position P){
    Position pre;
    for(pre=L;pre&&pre->Next!=P;pre=pre->Next);
    if(pre==NULL||P==NULL){
        printf ("Wrong Position for Deletion");
        return false;
    }
    else{
        pre->Next=P->Next;
        free(P);
        return true;
        }
    }