线性表-双向链表

1、单循环链表

　　将单链表中终端结点的指针端由空指针改为指向头节点，就使整个单链表形成一个环，这种头尾相接的单链表称为单循环链表，简称循环链表。

 其实循环链表和单链表的主要差异就在于循环的判断条件上，原来是判断 p->next是否为空，现在则是p->next不等于头结点，则循环未结束。

2、双向链表

　　双向链表是在单链表的每个结点中，再设置一个指向其前驱结点的指针。所以在双向链表中的结点有两个指针域，一个指向直接后继，另一个指向直接前驱。

　　双向链表是单链表扩展出来的结构，所以它的很多操作是和单链表相同的，比如求长度，查找元素，获得元素位置等。这些操作都只要涉及一个方向的指针即可，另一个指针多了也不能提供什么帮助。

//线性表的双向链表存储结构
typedef struct student
{
    int data;
    struct student *next; //直接后继指针
    struct student *pre; //直接前驱指针
}dnode;

1、编程实现双向链表的建立

dnode *creat()
{
    dnode *head, *p, *s;
    int x, cycle = 1;
    head = (dnode*)malloc(sizeof(dnode)); //头结点
    p = head; //p头指针
    while (cycle)
    {
        printf("
please input the data:");
        scanf("%d", &x);
        if (x != 0)
        {
            s = (dnode *)malloc(sizeof(dnode));
            s->data = x;
            printf("
%d", s->data);
            p->next = s;
            s->pre = p;
            p = s;
        }
        else cycle = 0;
    }
    head = head->next;
    head->pre = NULL;
    p->next = NULL;

    return head;
}

2、实现双向链表的删除

dnode *del(dnode *head, int num)
{
    dnode *p1;
    p1 = head; //没有头结点
    while (num != p1->data&&p1->next != NULL)
    {
        p1 = p1->next; //退出循环时 p1已经存储num地址
    }
    if (num == p1->data)
    {
        if (p1 == head) //头
        {
            head = head->next;
            head->pre = NULL;
            free(p1);
        }
        else if (p1->next == NULL) //尾
        {
            p1->pre->next = NULL;
            free(p1);
        }
        else   //中
        {
            p1->next->pre = p1->pre;
            p1->pre->next = p1->next;
        }
    }
    else
        printf("
 %d could not been found", num);
    return (head);

}

3、实现双向链表的插入

dnode *insert(dnode *head, int num)
{
    dnode *p0, *p1;
    p1 = head;
    p0 = (dnode *)malloc(sizeof(dnode));
    p0->data = num;
    while (p0->data > p1->data&&p1->next != NULL)
    {
        p1 = p1->next;
    }
    if (p0->data <= p1->data)
    {
        if (p1 = head) //头
        {
            p0->next = p1;
            p1->pre = p0;
            head = p0;
        }
        else //中
        {
            p0->next = p1;
            p0->pre = p1->pre;
            p1->pre->next = p0;
            p1->pre = p0;
        }
    }
    else //尾
    {
        p1->next = p0;
        p0->pre = p1;
        p0->next = NULL;
    }

    return (head);
}

 

4、实现双向链表的长度、打印

int length(dnode *head)
{
    dnode *p = head;
    int x = 0;
    while (p != NULL)
    {
        p = p->next;
        x++;
    }
    return x;
}

void print(dnode *head)
{
    dnode *p;int n;
    n = length(head);
    printf("
 Now ,these %d records are:
", n);
    p = head;
    if (head != NULL)
        while (p != NULL)
        {
            printf("
    %d", p->data);
            p = p->next;
        }
}

5、实现双向链表的创建、删除、插入、长度、打印等

void main()
{
    dnode *head;
    int del_num, insert_num;
    head = creat();
    print(head);

    printf("
please input the delete num:");
    scanf("%d", &del_num);
    head = del(head, del_num);
    print(head);

    printf("
please input the insert num:");
    scanf("%d", &insert_num);
    head = insert(head, insert_num);
    print(head);
    system("pause");
}