带头双向循环链表

    首先，我们来看一下带头双向循环链表的结构：

                      

目录

带头双向循环链表结点的定义：

相关操作接口：

 1、初始化 && 获取一个结点

2、销毁链表 

3、尾插

4、头插

5、指定元素查找

6、任意位置插入

7、 尾删

8、头删

9、任意位置删除

10、打印链表

附上完整代码：

---

带头双向循环链表结点的定义：

typedef int DataType;
typedef struct Node
{
	DataType data;
	struct Node* next;
	struct Node* prev;
}Node, *pNode, *pList;

相关操作接口：

 1、初始化 && 获取一个结点

        逻辑：因为实现的是带头结点的双向循环链表，所以初始化的时候，我们得到一个空的结点，它的 next 和 prev 都指向它自己。获取结点就是靠动态开辟空间。

pNode BuyNode(DataType d)
{
	pNode ptr = (pNode)malloc(sizeof(Node));
	if (ptr == NULL)
	{
		perror("BuyNode::malloc");
		return NULL;
	}
	ptr->data = d;
	ptr->next = NULL;
	ptr->prev = NULL;
	return ptr;
}

pList InitList()
{
	DataType d = 0;
	pNode head = BuyNode(d);
	head->next = head;
	head->prev = head;
	return head;
}

2、销毁链表 

     逻辑：遍历逐个销毁。

void DestoryList(pList plist)
{
	pNode cur = plist->next;
	pNode next = NULL;
	while (cur != plist)
	{
		next = cur->next;
		free(cur);
		cur = NULL;
		cur = next;
	}
}

3、尾插

   逻辑：记录好最后一个结点和头结点。

void PushBack(pList plist, DataType d)
{
	pNode head = plist;
	pNode tail = head->prev;
	//tail newnode head
	pNode newnode = BuyNode(d);;
	tail->next = newnode;
	newnode->prev = tail;

	newnode->next = head;
	head->prev = newnode;
}

4、头插

      逻辑：记录好第一个结点和头结点。

void PushFront(pList plist, DataType d)
{
	pNode first = plist->next;
	pNode newnode = BuyNode(d);
	//plist newnode first;
	plist->next = newnode;
	newnode->prev = plist;

	newnode->next = first;
	first->prev = newnode;
}

5、指定元素查找

      逻辑：遍历比较是否有指定元素，注意不要造成死循环。

pNode FindList(pList plist, DataType d)
{
	pNode cur = NULL;

	assert(plist);

	cur = plist->next;
	while (cur != plist)
	{
		if (cur->data == d)
		{
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}

6、任意位置插入

      逻辑：记录好指定位置的前一个结点和后一个结点。

void InsertList(pNode pos, DataType d)
{
	pNode newnode = NULL;
	pNode prev = NULL;

	assert(pos);

	prev = pos->prev;
	newnode = BuyNode(d);
	//prev newnode pos
	prev->next = newnode;
	newnode->prev = prev;

	newnode->next = pos;
	pos->prev = newnode;
}

7、 尾删

     逻辑：记录好头结点和倒数第二个结点。注意链表是否只有头结点，如果只有头结点，不可以删除。

void PopBack(pList plist)
{
	pNode tail = NULL;
	pNode prev = NULL;

	assert(plist&&plist->next != NULL);

#if 0     //方法一
	tail = plist->prev;
	prev = tail->prev;
	//plist ... prev tail
	plist->prev = prev;
	prev->next = plist;
	free(tail);
	tail = NULL;
#endif 

#if 1  //方法二
	EraseList(plist->prev);
#endif 

}

8、头删

     逻辑：记录好头结点和第二个结点。注意链表是否只有头结点，如果只有头结点，不可以删除。

void PopFront(pList plist)
{
	pNode first = NULL;
	pNode next = NULL;

	assert(plist&&plist->next != NULL);
	
#if 1    //方法一
	first = plist->next;
	next = first->next;
	//plist first next
	plist->next = next;
	next->prev = plist;
	free(first);
	first = NULL;
#endif

#if 0   //方法二
	EraseList(plist->next);
#endif
}

9、任意位置删除

    逻辑：记录好指定位置的前一个结点和后一个结点。注意链表是否只有头结点，如果只有头结点，不可以删除。

void EraseList(pNode pos)
{
	pNode prev = NULL;
	pNode next = NULL;

	assert(pos);

	prev = pos->prev;
	next = pos->next;
	//prev pos next
	prev->next = next;
	next->prev = prev;
	free(pos);
	pos = NULL;
}

10、打印链表

    逻辑：遍历打印。

void PrintList(pList plist)
{
	pNode cur = plist->next;
	while (cur != plist)
	{
		printf("%d -> ", cur->data);
		cur = cur->next;
	}
	printf("head\n");
}

总结：所有接口的实现，画图可以更好的让我们了解接口实现的逻辑，并且双向循环链表接口的实现都是很简单的，无论是插入删除，效率都是比较高的。

附上完整代码：

DList.h

#ifndef __DLIST_H__
#define __DLIST_H__

#include 
#include 
#include 

typedef int DataType;
typedef struct Node
{
	DataType data;
	struct Node* next;
	struct Node* prev;
}Node, *pNode, *pList;

pList InitList();
void DestoryList(pList plist);
pNode BuyNode(DataType d);
void PushBack(pList plist, DataType d);
void PushFront(pList plist, DataType d);
pNode FindList(pList plist, DataType d);
void InsertList(pNode pos, DataType d);
void PopBack(pList plist);
void PopFront(pList plist);
void EraseList(pNode pos);
void PrintList(pList plist);


#endif //__DLIST_H__

DList.c

#include "DList.h"

pNode BuyNode(DataType d)
{
	pNode ptr = (pNode)malloc(sizeof(Node));
	if (ptr == NULL)
	{
		perror("BuyNode::malloc");
		return NULL;
	}
	ptr->data = d;
	ptr->next = NULL;
	ptr->prev = NULL;
	return ptr;
}

pList InitList()
{
	DataType d = 0;
	pNode head = BuyNode(d);
	head->next = head;
	head->prev = head;
	return head;
}

void DestoryList(pList plist)
{
	pNode cur = plist->next;
	pNode next = NULL;
	while (cur != plist)
	{
		next = cur->next;
		free(cur);
		cur = NULL;
		cur = next;
	}
}

void PushBack(pList plist, DataType d)
{
	pNode head = plist;
	pNode tail = head->prev;
	//tail newnode head
	pNode newnode = BuyNode(d);;
	tail->next = newnode;
	newnode->prev = tail;

	newnode->next = head;
	head->prev = newnode;
}

void PushFront(pList plist, DataType d)
{
	pNode first = plist->next;
	pNode newnode = BuyNode(d);
	//plist newnode first;
	plist->next = newnode;
	newnode->prev = plist;

	newnode->next = first;
	first->prev = newnode;
}

pNode FindList(pList plist, DataType d)
{
	pNode cur = NULL;

	assert(plist);

	cur = plist->next;
	while (cur != plist)
	{
		if (cur->data == d)
		{
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}

void InsertList(pNode pos, DataType d)
{
	pNode newnode = NULL;
	pNode prev = NULL;

	assert(pos);

	prev = pos->prev;
	newnode = BuyNode(d);
	//prev newnode pos
	prev->next = newnode;
	newnode->prev = prev;

	newnode->next = pos;
	pos->prev = newnode;
}

void PopBack(pList plist)
{
	pNode tail = NULL;
	pNode prev = NULL;

	assert(plist&&plist->next != NULL);

#if 0     //方法一
	tail = plist->prev;
	prev = tail->prev;
	//plist ... prev tail
	plist->prev = prev;
	prev->next = plist;
	free(tail);
	tail = NULL;
#endif 

#if 1  //方法二
	EraseList(plist->prev);
#endif 

}

void PopFront(pList plist)
{
	pNode first = NULL;
	pNode next = NULL;

	assert(plist&&plist->next != NULL);
	
#if 1    //方法一
	first = plist->next;
	next = first->next;
	//plist first next
	plist->next = next;
	next->prev = plist;
	free(first);
	first = NULL;
#endif

#if 0   //方法二
	EraseList(plist->next);
#endif
}

void EraseList(pNode pos)
{
	pNode prev = NULL;
	pNode next = NULL;

	assert(pos);

	prev = pos->prev;
	next = pos->next;
	//prev pos next
	prev->next = next;
	next->prev = prev;
	free(pos);
	pos = NULL;
}

void PrintList(pList plist)
{
	pNode cur = plist->next;
	while (cur != plist)
	{
		printf("%d -> ", cur->data);
		cur = cur->next;
	}
	printf("head\n");
}

test.c

#include "DList.h"

void PushBackTest()
{
	pList plist;
	plist = InitList();
	PushBack(plist, 1);
	PushBack(plist, 2);
	PushBack(plist, 3);
	PushBack(plist, 4);
	PrintList(plist);      // 1  2  3  4 
	DestoryList(plist);
}

void PushFrontTest()
{
	pList plist = InitList();
	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	DestoryList(plist);
}

void FindListTest()
{
	pNode pos = NULL;
	pList plist = InitList();

	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	pos = FindList(plist, 3);
	if (pos == NULL)
	{
		printf("没找到\n");
	}
	else
	{
		printf("找到了:%d\n", pos->data);
	}
	DestoryList(plist);
}

void InsertListTest()
{
	pNode pos = NULL;
	pList plist = InitList();

	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	pos = FindList(plist, 3);
	if (pos == NULL)
	{
		printf("没找到\n");
	}
	else
	{
		InsertList(pos, 5);
		PrintList(plist);      // 4  5  3  2  1
	}
	DestoryList(plist);
}

void PopBackTest()
{
	pList plist = InitList();
	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	PopBack(plist);
	PrintList(plist);      // 4  3  2 
	PopBack(plist);
	PrintList(plist);      // 4  3  
	PopBack(plist);
	PrintList(plist);      // 4  
	PopBack(plist);
	PrintList(plist);      //
	DestoryList(plist);
}

void PopFrontTest()
{
	pList plist = InitList();
	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	PopFront(plist);
	PrintList(plist);      // 3  2  1
	PopFront(plist);
	PrintList(plist);      // 2  1
	PopFront(plist);
	PrintList(plist);      // 1
	PopFront(plist);
	PrintList(plist);      //
	DestoryList(plist);
}

void EraseListTest()
{
	pNode pos = NULL;
	pList plist = InitList();

	PushFront(plist, 1);
	PushFront(plist, 2);
	PushFront(plist, 3);
	PushFront(plist, 4);
	PrintList(plist);      // 4  3  2  1
	pos = FindList(plist, 3);
	if (pos == NULL)
	{
		printf("没找到\n");
	}
	else
	{
		EraseList(pos);
		PrintList(plist);      // 4  5  3  2  1
	}
	DestoryList(plist);
}

int main()
{
	PushBackTest();
	PushFrontTest();
	FindListTest();
	InsertListTest();
	PopBackTest();
	PopFrontTest();
	EraseListTest();

	return 0;
}