双链表

#include <iostream>
using namespace std;

struct node
{
    int data;
    node *next;
    node *pre;
};
//(1)创建双链表
node *create()
{
    node *head,*p,*s;
    int x;
    char c;
    head=new node;
    p=head;
    cout<<"please input the datas:"<<endl;
    while(cin>>x)
    {
        s=new node;
        s->data=x;
        p->next=s;
        s->pre=p;
        p=s;
        cin.get(c);
        if(c==‘\n‘) break;
    }
    head=head->next;
    head->pre=NULL;
    p->next=NULL;
    return head;
}
//(2)打印双链表
void print_list(node *head)
{
    node *p;
    p=head;
    while(p!=NULL)
    {
        cout<<p->data<<endl;
        p=p->next;
    }
}
//(3)双链表的删除节点操作
node *delete_node(node *head,int num)
{
    node *p;
    p=head;

    while(num!=p->data && p->next!=NULL)
    {
        p=p->next;             //跟单链表删除的区别：不需要一个指针p2来保存p的前驱节点
    }
    if(num==p->data)
    {
        if(p==head)
        {
            head=head->next;
            head->pre=NULL;
            delete p;
        }
        else if(p->next==NULL)
        {
            p->pre->next=NULL;
            delete p;
        }
        else
        {
            p->next->pre=p->pre;
            p->pre->next=p->next;
            delete p;
        }
    }
    else
        cout<<"not found"<<endl;
    return head;
}
//(4)双链表的插入操作
node *insert_node(node *head,int num)
{
    node *p=head;
    node *p2;
    p2=new node;
    while(p->data<num && p->next!=NULL)
    {
        p=p->next;
    }
    if(p->data>=num)
    {
        if(p==head)
        {
            p2->data=num;
            p->pre=p2;
            p2->next=p;
            p2->pre=NULL;

            head=p2;
        }
        else
        {
            p2->data=num;
            p2->pre=p->pre;
            p2->next=p;
            p->pre->next=p2;
        }
    }
    else
    {
        //p->next->data=num;
        //p->next->pre=p;
        //p->next->next=NULL;
        p2->data=num;
        p->next=p2;
        p2->pre=p;
        p2->next=NULL;
    }
    return head;
}

int main()
{
    node *p=create();
    print_list(p);
    //node *p1=delete_node(p,1);
    //print_list(p1);
    node *p2=insert_node(p,3);
    print_list(p2);
    return 0;
}