#include <stdio.h>
#include <stdlib.h>
typedef struct pointer
         { int info;
           struct pointer *LPTR;
           struct pointer *RPTR;
         } ds;
ds *l,*r,*q,*M;
int n,i,m,d;
void main()
{
    printf(" Nhap vao so phan tu muon nhap n= ");
    scanf("%d",&n);
    l=NULL;r=NULL;
    for(i=1;i<=n;i++)
    {
        q=(ds *)malloc(sizeof(ds));
        printf("\n phan tu thu %d ",i);
        scanf("%d",&q->info);
        if(l==NULL)
        {
            q->LPTR=NULL;
            q->RPTR=NULL;
            l=r=q;
        }
        else
        {
            q->LPTR=NULL;
            q->RPTR=l;
            l->LPTR=q;
            l=q;
        }
    }
    l=q;
    printf(" \n Day vua nhap:");
    for(i=1;i<=n;i++)
    {
        printf("%2d",q->info);
        q=q->RPTR;
    } printf("............ Day bi in nguoc nay");
    printf("\n hay nhap tu ban phim , thu tu phan tu muon tro toi \n");
    printf("chu y rang , so can nhap phai nho hon %d ",n);
    printf("m = ");
    do
    {
        scanf("%d",&m);
    }while(m>n);
    d=1;q=l;
    for(d=1;d<=m-1;d++)
    {
        q=q->RPTR;
    }
    M=q;
    printf(" Hay nhap gia tri phan tu muon bo sung sau con tro M ");
    q=(ds*)malloc(sizeof(ds));
    scanf("%d",&q->info);
    if(M==r)
    {
        q->RPTR=NULL;
        q->LPTR=M;
        M->RPTR=q;
        r=q;
    }
    else
    {
        q->LPTR=M;
        q->RPTR=M->RPTR;
        M->RPTR=q;
        q->RPTR->LPTR=q;
    }
    n++;
    printf("ta co danh sach sau khi them vao phan tu moi gom %d phan tu \n ",n);
    q=r;
    while(q!=NULL)
    {
        printf("%d",q->info);
        q=q->LPTR;
    }
    // xoa phan tu duoc tro boi M
    if((M==l)&&(M==r))
    {
        l=NULL;
        r=NULL;
    }
    if(M==l)
    {
        l=l->RPTR;
        l->LPTR=NULL;
        M->RPTR=NULL;
    }
    if(M==r)
    {
        r=r->LPTR;
        r->RPTR=NULL;
        M->LPTR=NULL;
    }
    else
    {
        M->LPTR->RPTR=M->RPTR;
        M->RPTR->LPTR=M->LPTR;
    }
    free(M);
    printf("\n danh sach sau khi da bo di 1 phan tu duoc tro boi con tro M la :\n ");
    q=r;
    while(q!=NULL)
    {
        printf("%d",q->info);
        q=q->LPTR;
    }

}