Doubly linked list【1月17日学习笔记】

//Doubly linked list
#include<iostream>
using namespace std;
struct node {
	int data;
	node* next;
	node* prev;
};//定义双向链表结构体
node* A;

node* getnewnode(int x) {
	node* temp = new node;
	temp->data = x;
	temp->prev = NULL;
	temp->next = NULL;
	return temp;
}//创建节点函数
void insertathead(int x) {
	node* temp = getnewnode(x);
	if (A == NULL) {
		A = temp;
		return;//不要忘记return//或者用else
	}//头指针为空时
	A->prev = temp;//1节点头部指向新节点
	temp->next = A;//新节点尾巴指向1节点
	A = temp;//头指针指向新节点//头指针与新节点不是双向，新节点头部默认指向NULL
}

void insertattail(int x) {
	node* temp = getnewnode(x);
	if (A == NULL) {
		A = temp;
	}
	else {
		node* run = A;
		while (run->next != NULL) {
			run = run->next;
		}
		run->next = temp;
		temp->prev = run;//新节点头部指向末节点
	}
}

void print() {
	node* run = A;
	while (run != NULL) {
		cout << run->data<<" ";
		run = run->next;
	}
	cout << endl;
}

void reverseprint() {
	if (A == NULL)  return;//empty list,exit
	node* run = A;
	while (run->next != NULL) {
		run = run->next;
	}//going to last node
	while (run != NULL) {
		cout << run->data << " ";
		run = run->prev;
	}//traversing backward uing prev pointer,结束时run指向NULL（run指向NULL：打印模式）
	cout << endl;
}
int main() {
	A = NULL;
	insertathead(2); print(); reverseprint();
	insertathead(4); print(); reverseprint();
	insertathead(6); print(); reverseprint();
	insertattail(-2); print(); reverseprint();
	insertattail(-4); print(); reverseprint();
	insertattail(-6); print(); reverseprint();
}