链表初解（二）——双链表的创建、删除、插入

#include<iostream>
using namespace std;

typedef struct student
{
int data;
struct student *next;
struct student *pre;
}dnode;

//建立双链表
dnode *create()
{
dnode *head, *p, *s;
int x;
head = (dnode *)malloc(sizeof(dnode));
p = head;
cout<<"\nInput the data : ";
while(1)
{
if(scanf("%d", &x) != EOF && x != 0)
{
s = (dnode *)malloc(sizeof(dnode));
s->data = x;
p->next = s;
s->pre = p;
p = s;
}
else break;
}
head = head->next;
head->pre = NULL;
p->next = NULL;
return head;
}

//双链表删除节点
dnode *del(dnode *head, int num)
{
dnode *p1;
p1 = head;
while(num != p1->data && p1->next != NULL)
p1 = p1->next;
if(num == p1->data)
{
if(head == p1)
{
head = head->next;
head->pre = NULL;
}/*此处的处理与单链表不同，因为双链表有两个方向，所以在定义时仅定义一个指针，
这使得当出现删除链表尾部时，由于NULL没有前驱，导致无法连接，所以要分开讨论。*/
else if(p1->next == NULL) p1->pre->next = NULL;
else
{//p1为最后一个节点，如没有上一个分支，则第二个语句会出错。
p1->pre->next = p1->next;
p1->next->pre = p1->pre;
}
free(p1);	//释放
}
else cout<<"There is no %d "<<num;
return head;
}

//双链表插入节点
dnode *insert(dnode *head, int num)
{
dnode *p0, *p1;
p1 = head;
p0 = (dnode *)malloc(sizeof(dnode));
p0->data = num;
while(num > p1->data && p1->next != NULL)
p1 = p1->next;
if(num <= p1->data)
{
if(head == p1)
{
p0->next = p1;
p1->pre = p0;
head = p0;
}
else
{
p1->pre->next = p0;
p0->pre = p1->pre;
p0->next = p1;
p1->pre = p0;
}
}
else
{//插入尾部~
p1->next = p0;
p0->next = NULL;
p0->pre = p1;
}
return head;
}

//计算表长
int length(dnode *head)
{
int n = 0;
while(head != NULL)
{
head = head->next;
n++;
}
return n;
}
//打印双链表
void print(dnode *head)
{
int n = length(head);
cout<<"Output the DoubleList ("<<n<<" records~) : ";
while(head != NULL)
{
if(head->next == NULL) cout<<head->data<<endl;
else cout<<head->data<<"<->";
head = head->next;
}
}
//排序函数同单链表，此处省略了~，默认输入为递增哈~
int main()
{
dnode *head;
//创建
head = create();
print(head);
//删除
int numD;
cout<<"\nDelete : ";
cin>>numD;
print(del(head, numD));
//插入
int numS;
cout<<"\nInsert : ";
cin>>numS;
print(insert(head, numS));
return 0;
}