include <stdio.h>

define ElementType int

typedef struct Node{
ElementType Date;
struct Node *Next;
}List;

List l, *Ptrl;

//求表长
int length(List *Ptrl)
{
List *p = Ptrl;
int j = 0;
while(p)
{
p = p -> Next;
j++;
}
return j;
}
//只能序号查找
List *FindKth(int k, List *Ptrl)
{
List *p = Ptrl;
int i = 1;
while(p != NULL && i< k)
{
p = p -> Next;
i++;
}
if(i == k)
return p;
else
return NULL;
}

//按值查找

List Find(ElementType x, List *Ptrl)
{
List *p = Ptrl;
while(p != NULL && p -> Date != x)
p = p -> Next;
return p;
}

//链表插入
List *Insert(ElementType x, int i, List *Ptrl)
{
List *p, *s;
if(i == 1)
{
s = (List *)malloc(sizeof(List));
s -> Date = x;
s -> Next = Ptrl;
return s;
}
p = FindKth(i-1, Ptrl);
if(p == NULL)
{
return NULL;
}
else
{
s = (List *)malloc(sizeof(List));
s -> Date = x;
s -> Next = p -> Next;
p -> Next = s;
return Ptrl;
}
}

//链表删除
List *Delete(int i, List *Ptrl)
{
List *p, *s;
if(i == 1)
{
s = Ptrl;
if(Ptrl != NULL)
Ptrl = Ptrl -> Next;
else
return NULL
free(s);
return Ptrl;
}
p = FindKth(i-1, Ptrl);
if(p == NULL)
{
//第n-1个几点不存在
return NULL;
}
else if(p -> Next == NULL)
{
//第n个几点不存在
return NULL;
}
else
{
s = p -> Next;
p -> Next = s -> Next;
free(s)
return Ptrl;
}
}