双链表

建立，插入，删除

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<conio.h>
using namespace std;

typedef struct student
{
	int data;
	struct student *next;
	struct student *pre;
}dnode;
//创建双链表
dnode* creat()
{
	dnode *head, *p, *s;
	int x;
	int cycle = 1;
	head = (dnode*)malloc(sizeof(dnode));
	p = head;
	while(cycle)
	{
		scanf_s("%d", &x);
		if(x != 0)
		{
			s = (dnode*)malloc(sizeof(dnode));
			s->data = x;
			p->next = s;
			s->pre = p;
			p = s;
		}
		else{
			cycle = 0;
		}
	}
	head = head->next;
	head->pre = nullptr;
	p ->next = nullptr;

	return head;
}

//删除节点
dnode* del(dnode* head, int num)
{
	dnode *p1, *p2;
	p1 = head;
	p2 = head;
	while(num != p1->data && p1->next != nullptr)
	{
		p1 = p1->next;
	}
	if(num == p1->data)
	{
		if(p1 == head)//头部
		{
			head = head->next;
			head->pre = nullptr;
			free(p1);
		}
		else if(p1->next == nullptr)//结尾
		{
			p1->pre->next = nullptr;
			free(p1);
		}
		else{//中间
			p1->next->pre = p1->pre;
			p1->pre->next = p1->next;
		}
	}
	else{
		printf("%d could not found.", num);
	}
	return head;
}

//插入节点
dnode* insert(dnode* head, int num)
{
	dnode *p0, *p1;//p0是要插入的节点，p1是遍历到的节点
	p1 = head;
	p0 = (dnode*)malloc(sizeof(dnode));
	p0->data = num;
	while(p0->data > p1->data  &&  p1->next != nullptr)
	{
		p1 = p1->next;
	}
	if(p0->data <= p1->data)
	{
		if(head == p1)
		{
			p0->next = p1;
			p1->pre = p0;
			p0->pre = nullptr;
			head = p0;
		}
		else{
			p1->pre->next = p0;
			p0->next = p1;
			p0->pre = p1->pre;
			p1->pre = p0;
		}
	}
	else{
		p1->next = p0;
		p0->pre = p1;
		p0->next = nullptr;
	}
	return head;
}

int length(dnode* head)
{
	int n = 0;
	dnode* p;
	p = head;
	while(p)
	{
		p = p->next;
		n++;
	}
	return n;
}
void print(dnode* head)
{
	dnode *p;
	int n;
	n = length(head);
	printf("These %d records are:\n", n);
	p = head;
	if(head != nullptr)
	{
		while(p)
		{
			printf("%d ", p->data);
			p = p->next;
		}
	}
}

int main()
{
	dnode *head;
	head = creat();
	print(head);
	cout << "删除1:" << endl;
	head = del(head, 1);
	print(head);
	cout << "插入1:" << endl;
	head = insert(head,1);
	print(head);
	return 0;
}