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;
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
#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;
}
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