数据结构：循环双向链表

#include<stdio.h>
#include<stdlib.h>

typedef struct plink
{
    int data;
    struct plink * prev;
    struct plink * next;
    
}PlinkNode, * PlinkList;

PlinkList Tail_Plinklist(int e);
PlinkList Heard_Plinklist(int e);
void Insert_Plinklist(PlinkList H,int pos,int e);
int Delete_Plinklist(PlinkList H,int pos);
void Print_Plinklist(PlinkList PL);
int GetElem_Plinklist(PlinkList PL,int pos);

PlinkList Tail_Plinklist(int e)
{
    PlinkList H = (PlinkList)malloc(sizeof(PlinkNode));
    PlinkList q;
    int d;
    q = H;
    q->next = H;
    q->prev = H;
    for(int i = 0;i < e;i++)
    {
        scanf("%d",&d);
        PlinkList p = (PlinkList)malloc(sizeof(PlinkNode));
        p->data = d;
        p->next = q->next;
        q->next->prev = p;
        q->next = p;
        p->prev = q;
        q = q->next; 
    }
    return H;
}

PlinkList Heard_Plinklist(int e)
{
    PlinkList H = (PlinkList)malloc(sizeof(PlinkNode));
    PlinkList q;
    int d;
    H->next = H;
    H->prev = H;
    if(e >= 1)
    {
        scanf("%d",&d);
        q = (PlinkList) malloc (sizeof(PlinkNode));
        q->data = d;
        q->next = H->next;
        H->next = q;
        q->prev = H;
        H->prev = q;
    }
    
    for (int i = 0; i < e-1; i++)
    {
        scanf("%d",&d);
        q = (PlinkList) malloc (sizeof(PlinkNode));
        q->data = d;
        q->next = H->next;
        H->next = q;
        q->prev = H;
    }
    return H;
    
}

void Insert_Plinklist(PlinkList H,int pos,int e)
{
    PlinkList L,p;
    L = H;
    p = (PlinkList)malloc(sizeof(PlinkNode));
    p->data = e;
    for (int i = 1; i < pos; i++)
    {
        L = L->next;
    }
    p->next = L->next;
    L->next->prev = p;
    L->next = p;
    p->prev = L;
}

int Delete_Plinklist(PlinkList H,int pos)
{
    PlinkList L,p;
    int d;
    L = H;
    for (int i = 1; i < pos; i++)
    {
        L = L->next;
    }
    p = L->next;
    L->next = p->next;
    p->next->prev = L;
    d = p->data;
    p->next = NULL;
    p->prev = NULL;
    free(p);
    return d; 
}

int GetElem_Plinklist(PlinkList PL,int pos)
{
    PlinkList L;
    int d = 0;
    L = PL;
    for (int i = 0; i < pos; i++)
    {
        L = L->next;
    }
    d = L->data;
    return d;
}

void Print_Plinklist(PlinkList PL)
{
    PlinkList q = PL->next;
    while (q != PL)
    {
        printf("%d ",q->data);
        q = q->next;
    }
    printf("\n");
}

int main()
{
    PlinkList L;
    L = Heard_Plinklist(5);
    Insert_Plinklist(L,3,99);
    Print_Plinklist(L);
    int num = Delete_Plinklist(L,2);
    Print_Plinklist(L);
    int n = GetElem_Plinklist(L,4);
    printf("%d",n);
    system("pause");
    return 0;
}