一个简单双向链表-内容倒置

---

###双向链表比基础链表结构多了一个前置指针。

struct node {
    int data;
    node *p;
    node *n;
};

###链表对象

struct dd_link
{
    node *head;
    node *tail;
};

###添加元素

void add(dd_link *link,node *n,bool first = false)
{
    //需要复制 node内容需要malloc 这里不做内容复制只做逻辑处理
    if (link->head==NULL)
    {
        link->head = link->tail = n;
    }
    else
    {
        if (first)
        {
            node* tmp = link->head;
            link->head = n;
            n->n = tmp;
            tmp->p = n;

        }else {
            node* tmp = link->tail;
            link->tail->n = n;
            n->p = tmp;
            link->tail = n;
        }
    }
}

###内容倒置 逻辑很简单就是把 前置和后继 指针做一下交换

//交换
void swap(node *&x, node *&y)
{
    
    node *temp = x; 
    x = y;
    y = temp;
}
//倒置
void rever(dd_link *link)
{
    node* n, *old_head;n = old_root = link->head;
    while (n != NULL)
    {
        node *tmp_n = n;
        n = n->n;
        swap(tmp_n->p,tmp_n->n);
    } 
    link->head = link->tail;
    link->tail = old_head;
}

测试

 void main( void )   
{   
     dd_link link = {};
     link.root = NULL;
     link.tail = NULL;
     
     node node1 = {};
     node1.data = 1;

     node node2 = {};
     node2.data = 2;
     
     node node3 = {};
     node3.data = 3;

     add(&link, &node2);
     add(&link, &node1,true);
     add(&link, &node3);

     loop_print(&link);
     rever(&link);
     printf("after rever\n");
     loop_print(&link);
}