双向带头循环链表
1. 程序表和链表
（1）程序表
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长处：
a、反对随机拜访，很多算法都须要随机拜访（快排、二分）
b、cpu 高速缓存命中率更高（cpu 读数据时，先去找缓存，如果没有就去内存把数据加载到缓存。在加载时它不是只加载一个数据，而是左近一片数据，所以如果是数组，它的数据是间断的，都会被加载到缓存了）
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毛病：
a、除了最初地位，其余地位插入删除效率低b、空间增容须要工夫和可能会节约空间
（2）双向带头循环链表
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长处：
a、任意地位插入删除效率 O(1)b、按需申请开释空间，不浪费时间和空间
c、cpu 高速缓存命中率更低（还会净化缓存，让缓存有很多无用的数据）
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毛病：
a、不反对随机拜访，一些算法无奈应用（快排、二分）b、链表存数据还得存储指针
2. 模仿实现
#define _CRT_SECURE_NO_WARNINGS 1
#include"list.h"
struct node* buy_node(type x)
{struct node* newnode = (struct node*)malloc(sizeof(struct node));
newnode->data = x;
newnode->next = NULL;
newnode->prev = NULL;
return newnode;
}
struct node* list_init()
{struct node* newnode = buy_node(-1);
newnode->next = newnode;
newnode->prev = newnode;
return newnode;
}
// 不须要二级指针，因为有哨兵，只是扭转上一个结点的值
void list_push_back(struct node* head, type x)
{/*assert(head);
struct node* newnode = buy_node(x);
struct node* tail = head->prev;
tail->next = newnode;
newnode->prev = tail;
newnode->next = head;
head->prev = newnode;*/
// 也能够复用
list_insert(head, x);// 在 Head 的后面插入一个节点就是尾插
}
void list_pop_back(struct node* head)
{//assert(head);
//assert(head->next != head);// 这才是起码有一个节点，而不是 assert(head->next)
//struct node* tail = head->prev;
//struct node* newtail = tail->prev;
//free(tail);
//newtail->next = head;
//head->prev = newtail;
// 复用
list_erase(head->prev);
}
void list_push_front(struct node* head, type x)
{/*assert(head);
struct node* newnode = buy_node(x);
struct node* next = head->next;
newnode->prev = head;
head->next = newnode;
newnode->next = next;
next->prev = newnode;*/
// 复用
list_insert(head->next, x);
}
void list_pop_front(struct node* head)
{/*assert(head);
struct node* next = head->next->next;
free(head->next);
head->next = next;
next->prev = head;*/
// 复用
list_erase(head->next);
}
void list_print(struct node* head)
{
struct node* t = head->next;
while (t != head)
{printf("%d", t->data);
t = t->next;
}
printf("\n");
}
struct node* list_find(struct node* head, type x)
{assert(head);
struct node* t = head->next;
while (t != head)
{if (t->data == x)
{return t;}
t = t->next;
}
return NULL;
}
// 插入 pos 之前的那个结点
void list_insert(struct node* pos, type x)
{assert(pos);
struct node* newnode = buy_node(x);
struct node* prev = pos->prev;
prev->next = newnode;
newnode->prev = prev;
newnode->next = pos;
pos->prev = newnode;
}
void list_erase(struct node* pos)
{assert(pos);
struct node* prev = pos->prev;
struct node* next = pos->next;
free(pos);
prev->next = next;
next->prev = prev;
}
void list_destroy(struct node* head)
{assert(head);
struct node* t = head;
while (t != head)
{
struct node* next = t->next;
free(t);
t = next;
}
free(head);
head = NULL;// 没有用其实
// 下面这么写无奈扭转 head 的值，不能让它变成 NULL，用二级指针才能够；然而要放弃接口一致性, 用一级指针就须要本人写 head = NULL
}
/*void list_destroy(struct node** phead)
{assert(*phead);
struct node* t = *phead;
while (t != *phead)
{
struct node* next = t->next;
free(t);
t = next;
}
free(*phead);
*phead = NULL;
}*/