6-6 帶頭結點的鏈式表操作集（20 分）

本題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

List MakeEmpty(){
  List head = (List)malloc(sizeof(List));
  head->Next = NULL;
  return head;
}

Position Find( List L, ElementType X ){
  List head = L->Next;
  while(head){
    if(head->Data == X){
      return head;
    }
    head = head->Next;
  }
  return ERROR;
}

bool Insert( List L, ElementType X, Position P ){
  List head = L;
  while(head){
    if(head->Next == P){
      List Node = (List)malloc(sizeof(List));
      Node->Data = X;
      Node->Next = head->Next;
      head->Next = Node;
      return true;
    }
    head = head->Next;
  }
  printf("Wrong Position for Insertion\n");
  return false;
}

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