数据结构----双向不循环链表

以下内容只是学习记录：

一、背景

　　之前讨论的链式存储结构的节点中只有一个指示直接后继的指针域，因此，从某个节点出发只能顺时针往后查找其他节点。若要查询节点的直接前驱，则需要从表头触发，若是单循环则需要查找一个周期，换句话说，在单链表中，NextElem的执行时间为O(1)，而PriorElem的执行时间为O(n)。为克服这个缺点，可以使用双向链表。

二、定义

　　顾名思义，在双向链表的节点中有两个指针域，一个指向直接后继，一个指向直接前驱，结构体定义如下：

#define ElemType int
 
typedef struct Node
{
    ElemType data;
    struct Node *prior;//指向前驱的指针
    struct Node *next;//指向后继的指针
}Node, *PNode;<br><br>

typedef struct List
{
    PNode first;//头节点
    PNode last;//尾节点
    int size;//链表数据长度
 
}List;

三、代码实现

　　1、链表初始化

void InitDList(List *list)
{
    Node *s = (Node *)malloc(sizeof(Node));
    assert(s!=NULL);
    list->first = list->last = s;
    list->last->next = NULL;
    list->first->prior = NULL;
    /*list->last->prior = NULL;
    list->first->next = NULL;*/  //这两行多余 因为first和last指向同一个地址
    list->size = 0;
}

　　2、链表测试函数编写　

#include "DList.h"
 
void main()
{
    List mylist;
    InitDList(&mylist);
    ElemType Item;
    Node *p = NULL;
    int select = 1;
    while (select)
    {
        printf("***************************************************\n");
        printf("*   [1] push_back               [2] push_front      *\n");
        printf("*   [3] show_list               [4] pop_back        *\n");
        printf("*   [5] pop_front               [6] insert_val      *\n");
        printf("*   [7] find                    [8] length      *\n");
        printf("*   [9] delete_val              [10] sort       *\n");
        printf("*   [11] reverse                [12] clear      *\n");
        printf("*   [13] destroy                [0] quit_system     *\n");
        printf("***************************************************\n");
        printf("请选择：>");
        scanf("%d", &select);
        if (select == 0)
            break;
        switch (select)
        {
        case 1:
            printf("请输入要插入的数据（-1结束）：");
            while (scanf("%d", &Item), Item != -1)
            {
                push_back(&mylist, Item);
            }
 
            break;
        case 2:
            printf("请输入要插入的数据（-1结束）：");
            while (scanf("%d", &Item), Item != -1)
            {
                //push_front(&mylist, Item);
            }
            break;
        case 3:
            show_list(&mylist);
            break;
        case 4:
            pop_back(&mylist);
            break;
        case 5:
            pop_front(&mylist);
            break;
        case 6:
            printf("请输入要插入的数据：");
            scanf("%d", &Item);
            insert_val(&mylist, Item);
            break;
        case 7:
            printf("请输入要查找的数据：");
            scanf("%d", &Item);
            p = find(&mylist, Item);
            if (p == NULL)
            {
                printf("要查找的数据在链表中不存在\n");
            }
            else
            {
                printf("要查找的数据为：%d", p->data);
            }
            break;
        case 8:
            printf("链表的长度为：%d\n", length(&mylist));
            break;
        case 9:
            printf("请输入要删除的值：");
            scanf("%d", &Item);
            delete_val(&mylist, Item);
            break;
        case 10:
            sort(&mylist);
            break;
        case 11:
            reverse(&mylist);
            break;
        case 12:
            clear(&mylist);
            break;
        case 13:
            destroy(&mylist);
            break;
        case 14:
            break;
        default:
            printf("输入的命令错误，请重新输入.\n");
            break;
        }
    }
    //destroy(&mylist);
}

　　3、链表功能函数编写

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#include "DList.h"
 
void InitDList(List *list)
{
    Node *s = (Node *)malloc(sizeof(Node));
    assert(s!=NULL);
    list->first = list->last = s;
    list->last->next = NULL;
    list->first->prior = NULL;
    /*list->last->prior = NULL;
    list->first->next = NULL;*/  //这两行多余 因为first和last指向同一个地址
    list->size = 0;
}
 
Node* _buynode(ElemType x)
{
    Node *s = (Node *)malloc(sizeof(Node));
    assert(s!=NULL);
    s->data = x;
    s->next = NULL;
    s->prior = NULL;
    return s;
}
void push_back(List *list, ElemType x)
{
    Node *s = _buynode(x);
    s->prior = list->last;
    list->last->next = s;
    list->last = s;
    list->size++;
}
 
void push_front(List *list, ElemType x)
{
    Node *s = _buynode(x);
    if (list->first == list->last)
    {
        s->prior = list->first;
        list->first->next = s;
        list->last = s;
    }
    else
    {
        s->next = list->first->next;
        s->next->prior = s;
        s->prior = list->first;
        list->first->next = s;
    }
     
    list->size++;
}
 
 
void show_list(List *list)
{
    Node *p = list->first->next;
    while (p != NULL)
    {
        printf("%d->",p->data);
        p = p->next;
    }
    printf("Null.");
}
 
void pop_back(List *list)
{
    if (list->size == 0)
        return;
    Node *p = list->last;
    p->prior->next = NULL;
    list->last = p->prior;
    free(p);
    p = NULL;
    list->size--;
}
 
void pop_front(List *list)
{
    if (list->size == 0)
        return;
    Node *p = list->first->next;
    if (p == list->last)
    {
        list->last = list->first;
        list->first->next = NULL;
        free(p);
        p = NULL;
    }
    else
    {
        list->first->next = p->next;
        p->next->prior = list->first;
        free(p);
        p = NULL;
    }
    list->size--;
}
 
void insert_val(List *list, ElemType x)//前提是数据有序
{
    Node *p = list->first;
    while (p->next != NULL && p->next->data <= x)
    {
        p = p->next;
    }
    if (p->next == NULL)
    {
        push_back(list, x);
    }
    else
    {
        Node *q = _buynode(x);
        q->next = p->next;
        p->next->prior = q;
        q->prior = p;
        p->next = q;
        list->size++;
    }
}
 
Node *find(List *list, ElemType key)
{
    Node *p = list->first;
    while (p->next != NULL && p->next->data != key)
        p = p->next;
    return p->next;
}
 
int length(List *list)
{
    return list->size;
}
 
void delete_val(List *list, ElemType key)
{
    if (list->size == 0)
        return;
    Node *p = find(list, key);
    if (p == NULL)
    {
        printf("要删除的值不存在。\n");
        return;
    }
    if (p == list->last)
    {
        list->last = p->prior;
        list->last->next = NULL;
        free(p);
        p = NULL;
    }
    else
    {
        p->prior->next = p->next;
        p->next->prior = p->prior;
        free(p);
        p = NULL;
    }
    list->size--;
}
 
void sort(List *list)
{
    if (list->size == 0 || list->size == 1)
        return;
    Node *s = list->first->next;
    Node *q = s->next;
    list->last = s;
    list->last->next = NULL;
    while (q != NULL)
    {
        s = q;
        q = q->next;
        Node *p = list->first;
        while (p->next != NULL && p->next->data <= s->data)
            p = p->next;
        if (p->next == NULL)
        {
            s->prior = list->last;
            s->next = NULL;
            list->last->next = s;
            list->last = s;
            list->size++;
        }
             
             
        else
        {
            s->next = p->next;
            s->next->prior = s;
            s->prior = p;
            p->next = s;
            list->size++;
        }
    }
}
 
void reverse(List *list)
{
 
    if (list->size == 0 || list->size == 1)
        return;
    Node *s = list->first->next;
    Node *q = s->next;
    list->last = s;
    list->last->next = NULL;
    while (q != NULL)
    {
        s = q;
        q = q->next;
        s->next = list->first->next;
        list->first->next->prior = s;
        s->prior = list->first;
        list->first->next = s;
    }
}
 
void clear(List *list)
{
    if (list->size == 0)
        return;
    Node *p = list->first->next;
    while (p != NULL)
    {
        if (p == list->last)
        {
            list->last = list->first;
            list->last->next = NULL;
 
        }
        else
        {
            p->next->prior = list->first;
            list->first->next = p->next;
        }
        free(p);
        p =list->first->next;
    }
    list->size = 0;
 
}
 
 
void destroy(List *list)
{
    clear(list);
    free(list->first);
    list->first = list->last = NULL;
}