【寒假作业】day2.4

1.

int length(linklist head)
{
    int len=0;
    linklist p=head;
    while(p)
    {
        p=p->next;
        len++;
    }
    return len;
    
}
void output(linklist head)
{
    if(head==NULL)
    {
        puts("EMPTY");
        return;
    }
    linklist p=head;
    while(p)
    {
        printf("%-5d",p->data);
        p=p->next;
    }
    puts("");
}
linklist insert_head(linklist head,datatype element)
{
    linklist s=create_node();
    s->data=element;
    if(head==NULL)
        head=s;
    else
    {
        s->next=head;
        s->prev=NULL;
        head=s;
    }
    return head; 
}
linklist insert_rear(linklist head,datatype element)
{
    linklist s=create_node();
    s->data=element;
    if(head==NULL)
        head=s;
    else
    {
        linklist p=head;
        while(p->next)
        {
            p=p->next;
        }
        p->next=s;
        s->next=NULL;
        s->prev=p;
    }
    return head;
}
linklist del_head(linklist head)
{
    if(head==NULL)
        return head;
    else if(head->next==NULL)
    {
        linklist del=head;
        head=head->next;
        head->prev=NULL;
        free(del);
        del=NULL;
        return head;
    }
}
linklist del_rear(linklist head)
{
    if(head==NULL)
    return head;
    else if(head->next==NULL)
    {
        free(head);
        head=NULL;
        return head;
    }
    else
    {
        linklist del=head;
        while(del->next)
        {
        del=del->next;
        }
        del->prev->next=NULL;
        free(del);
        del=NULL;
        return head;
    }
}

linklist insert_pos(linklist head,int pos,datatype element)
{
    linklist s=create_node();
    s->data=element;
    if(head==NULL || pos==1)
        head=insert_head(head,element);
        return head;
    if(pos<1 || pos>length(head)+1)
    {
        puts("ERROR");
        return head;
    }
    else
    {
        linklist p=head;
        for(int i=1;i<pos-1;i++)
        {
            p=p->next;
        }
        s->next=p->next;
        s->prev=p;
        p->next->prev=s;
        p->next=s;
        return head;
    }
}
linklist del_pos(linklist head,int pos)
{
    if(head==NULL)
        return head;
    if(pos<1 || pos>length(head)+1)
    {
        puts("ERROR");
        return head;
    }
    else
    {
        if(pos==1)
        {
            head=del_head(head);
            return head;
        }
        else if(pos==length(head))
        {
            head=del_rear(head);
            return head;
        }
        else
        {
            linklist p=head;
            for(int i=1;i<pos;i++)
            {
                p=p->next;
            }
            p->prev->next=p->next;
            p->next->prev=p->prev;
            free(p);
            p=NULL;
            return head;
        }
    }
}
linklist change_pos(linklist head,int pos,datatype element)
{
 
    if(pos<1 || pos>length(head)+1)
    {
        puts("ERROR");
        return head;
    }
    linklist p=head;
    for(int i=1;i<pos;i++)
    {
        p=p->next;
    }
    p->data=element;
    return head;
 
 
}
void find_pos(linklist head,int pos)
{
    if(pos<1 || pos>length(head)+1)
    {
        puts("ERROR");
        return;
    }    
    linklist p=head;
    for(int i=1;i<pos;i++)
    {
        p=p->next;
    }
    printf("%d\n",p->data);
    return;
}

3.栈是先进后出的思想，队列是先进先出的思想

4.堆区释放内存时，指针未指向释放内存首地址