链表随笔之双向链表

 和单链表差不多，就不多说了。

特别注意在插入和删除链表元素操作时，仔细考虑该元素与相邻元素的前向指针、和后续指针的改变。

struct Node 
{
    int val;
    Node* pret;
    Node* next;
};

Node* cre_list(int n)         //创建双向链表 n代表元素个数
{
    Node* head_temp = NULL;
    if (n > 0)
    {
        Node* head = new Node;
        head->val = rand()%100;
        head->pret = NULL;
        head->next = NULL;
        head_temp = head;

        for (int i = 1 ; i < n;++i)
        {
            Node* temp = new Node;
            temp->val = rand()%100;
            temp->next = NULL;
            temp->pret = head;
            head->next = temp;
            head = temp;
        }
    }
    return head_temp;
}
int get_len(Node* head)           //获得双向链表长度
{
    int num = 0 ;
    Node* temp = head;
    while (temp != NULL)
    {
        ++num;
        temp = temp->next;
    }
    return num;
}
void display(Node* head)          //输出元素
{
    Node* temp = head;
    while (temp != NULL)
    {
        cout<<temp->val<<' ';
        temp = temp->next;
    }
    cout<<endl;
}
void charu(Node* &head,int n,int pos) //插入元素
{
    int len = get_len(head);
    if (pos < 0||pos > len)
    {
        return;
    }
    Node* temp = head;
    Node* new_one = new Node;
    new_one->val = n;
    if (pos == 0)                     //插入在第一个位置 3
    {
        new_one->pret = NULL;
        new_one->next = temp;
        temp->pret = new_one;
        head = new_one;
    }
    else if (pos == len)            //插入到最后一个位置 3
    {
        new_one->next = NULL;
        for (int i = 1; i < pos;++i)
        {
            temp = temp->next;
        }
        temp->next = new_one;
        new_one->pret = temp;
    }
    else                                //插入到中间 4
    {
        for (int i = 1 ; i < pos;++i)
        {
            temp = temp->next;
        }
        Node* temp2 = temp->next;
        new_one->next = temp2;
        temp2->pret = new_one;
        new_one->pret = temp;
        temp->next = new_one;
    }
}
void del_node(Node* &head,int n)   //删除节点
{
    Node* temp = head;
    if (head->val == n)         //删除的是头节点  2
    {
        temp = head->next;
        temp->pret = NULL;
        delete head;
        head = temp;
    }
    else                                  //
    {
        temp = temp->next;
        while (temp != NULL)
        {
            if (temp->val == n)                 
            {
                if (temp->next == NULL)               //删除的是最后个节点 1
                {
                    Node* temp2 = temp->pret;
                    temp2->next = NULL;
                    delete temp;
                }
                else                                //删除中间部分的节点  2
                {
                    Node* temp2 = temp->next;
                    Node* temp1 = temp->pret;
                    temp1->next = temp2;
                    temp2->pret = temp1;
                    delete temp;
                }
                return;
            }
            temp = temp->next;
        }
    }
    return;
}