數據結構—雙向鏈表

雙向鏈表也叫雙鏈表，是鏈表的一種，它的每個數據結點中都有兩個指針，分別指向直接後繼和直接前驅。所以，從雙向鏈表中的任意一個結點開始，都可以很方便地訪問它的前驅結點和後繼結點，時間複雜度爲O(1)。

雙鏈表具有以下優點：

1、刪除單鏈表中的某個結點時，一定要得到待刪除結點的前驅，得到該前驅有兩種方法，第一種方法是在定位待刪除結點的同時一路保存當前結點的前驅。第二種方法是在定位到待刪除結點之後，重新從單鏈表表頭開始來定位前驅。儘管通常會採用方法一。但其實這兩種方法的效率是一樣的，指針的總的移動操作都會有2*i次。而如果用雙向鏈表，則不需要定位前驅結點。因此指針總的移動操作爲i次。

2、查找時也一樣，我們可以借用二分法的思路，從head（首節點）向後查找操作和last（尾節點）向前查找操作同步進行，這樣雙鏈表的效率可以提高一倍。

可是爲什麼市場上單鏈表的使用多於雙鏈表呢？

從存儲結構來看，每個雙鏈表的節點要比單鏈表的節點多一個指針，而長度爲n就需要 n*length（這個指針的length在32位系統中是4字節，在64位系統中是8個字節） 的空間，這在一些追求時間效率不高應用下並不適應，因爲它佔用空間大於單鏈表所佔用的空間；這時設計者就會採用以時間換空間的做法，這時一種工程總體上的衡量。

代碼實現：

#define _CRT_SECURE_NO_WARNINGS
#include "iostream"

using namespace std;

typedef struct Person  //數據
{
	int number;
	char name[32];
}DATATYPE;

typedef struct Node	//結點
{
	DATATYPE data;
	Node *pri;
	Node *next;
}linkNode;

typedef struct List		//鏈表
{
	linkNode *head;
	int clen;
}linkLIst;

//鏈表初始化
linkLIst * initList()
{
	linkLIst *tmp = new linkLIst;
	if (NULL == tmp)
	{
		perror("list_init Linklist");
		exit(1);
	}

	tmp->clen = 0;
	tmp->head = NULL;
	return tmp;
}

//頭插
int insertHead(linkLIst *mlist,DATATYPE *data)
{
	linkNode *newnode = new linkNode;	//創建要添加的結點
	newnode->next = NULL;
	newnode->pri  = NULL;

	if (NULL == newnode)
	{
		perror("insertHead newnode");
		return 1;
	}
	
	newnode->data = *data;
	newnode->next = mlist->head;

	mlist->head = newnode;
	mlist->clen++;

	return 0;
}

//尾插
int insertTail(linkLIst *mlist, DATATYPE *data)
{
	linkNode *newnode = new linkNode;		//創建要添加的結點
	if (NULL == newnode)
	{
		perror("insrtTail newnode");
		return 1;
	}

	newnode->data = *data;
	newnode->next = NULL;
	newnode->pri = NULL;

	if (NULL == mlist->head)
	{
		mlist->head = newnode;
	}
	else
	{
		linkNode* tmp = mlist->head;

		while (tmp->next)
		{
			tmp = tmp->next;
		}

		tmp->next = newnode;
		newnode->pri = tmp;
	}	
	
	mlist->clen++;
	return 0;
}

//查找
linkNode* findList(linkLIst *mlist,char *pname)
{
	linkNode *tmp = mlist->head;
	while (tmp)
	{
		if (0 == strcmp(tmp->data.name,pname))
		{
			return tmp;
		}
		tmp = tmp->next;
	}
	return NULL;
}

//刪除元素
int delList(linkLIst *mlist, char *pname)
{
	if (NULL == mlist->head)			//判斷鏈表是否爲空
	{
		cout << "鏈表已爲空" << endl;
		return 1;
	}

	if (NULL == mlist->head->next)				//判斷是否只有表頭
	{
		if (0 == strcmp(mlist->head->data.name,pname))
		{
			delete mlist->head;
			mlist->head = NULL;
		}
		else
		{
			cout << "未查到。。。" << endl;
			return 1;
		}
	}
	else
	{
		linkNode *p = mlist->head;
		linkNode *q = mlist->head;

		while (p)
		{
			if (0 == strcmp(p->data.name,pname))		
			{
				if (p == q)					//判斷是否爲表頭
				{
					mlist->head = p->next;
					p->next->pri = NULL;
				}
				else
				{
					q->next = p->next;
					p->next->pri = q;
				}
				delete p;
				p = NULL;
				mlist->clen--;
				return 0;
			}
			else
			{
				q = p;
				p = p->next;			
			}
		}
	}
	cout << "未找到要刪除的元素。。。" << endl;
	return 1;
}

//鏈表逆序
int reverseList(linkLIst *mlist)
{
	linkNode *p = mlist->head->next;
	linkNode *q = mlist->head;

	while (p)
	{
		q->next = p->next;
		if (p->next)
		{
			p->next->pri = q;
		}
		p->next = mlist->head;
		p->pri = NULL;
		mlist->head = p;
		p = q->next;
	}

	return 0;
}

//鏈表排序
int sortList(linkLIst *mlist)
{
	if (NULL == mlist->head)
	{
		cout << "鏈表爲空" << endl;
		return 1;
	}

	if (NULL == mlist->head->next)
	{
		cout << "鏈表只有一個表頭" << endl;
		return 0;
	}
	else
	{
		linkNode *p, *q, temp;
		q = mlist->head;
		while (q->next != NULL)
		{
			p = q->next;
			while (p != NULL)
			{
				if (p->data.number < q->data.number)
				{
					temp.data = p->data;
					p->data = q->data;
					q->data = temp.data;
				}
				p = p->next;
			}
			q = q->next;
		}	
	}

	cout << "排序完成" << endl;
	return 0;
}

//修改鏈表元素
int updataList(linkLIst *mlist,char *oldname,char *newname)
{
	linkNode *temp;
	temp = findList(mlist,oldname);
	strcpy(temp->data.name, newname);
	return 0;
}

//銷燬鏈表
int destoryList(linkLIst *mlist)
{
	linkNode *tmp = mlist->head;
	while (mlist->head)			//逐個刪除每個結點
	{
		tmp = mlist->head;
		mlist->head = tmp->next;
		delete tmp;
	}

	tmp = NULL;
	delete mlist;
	mlist = NULL;
	cout << "釋放完成" << endl;
	return 0;
}

//打印鏈表
int showList(linkLIst *mlist)
{
	linkNode *tmp = mlist->head;
	while (tmp)
	{
		cout << "ID:" << tmp->data.number << " " << "名字：" << tmp->data.name << endl;
		tmp = tmp->next;
	}

	return 0;
}

int main()
{
	linkLIst *m_list = initList();
	DATATYPE data1 = { 1,"劉德華" };
	DATATYPE data2 = { 0,"周潤發" };

	cout << "頭插：" << endl;
	insertHead(m_list, &data1);
	insertHead(m_list, &data2);	
	cout << "當前鏈表長度：" << m_list->clen << endl;
	showList(m_list);

	DATATYPE data3[3] = {
		{2,"張學友"},
		{3,"郭富城"},
		{4,"黎明"}
	};
	DATATYPE data4 = { 1,"周星馳" };
	cout << "尾插：" << endl;

	insertTail(m_list, &data3[0]);
	insertTail(m_list, &data3[1]);
	insertTail(m_list, &data3[2]);
	insertTail(m_list, &data4);

	sortList(m_list);
	cout << "當前鏈表長度：" << m_list->clen << endl;
	showList(m_list);

	cout << "---------------------------------------------------" << endl;
	cout << "鏈表逆序：" << endl;
	reverseList(m_list);
	cout << "鏈表長度：" << m_list->clen << endl;
	showList(m_list);

	cout << "---------------------------------------------------" << endl;
	cout << "查找元素：" << endl;
	linkNode* res = findList(m_list, "劉德華");
	if (NULL != res)
	{
		cout << "ID：" << res->data.number << " " << "姓名：" << res->data.name << endl;
	}
	else
	{
		cout << "未找到。。。" << endl;
	}

	cout << "---------------------------------------------------" << endl;
	cout << "刪除元素：" << endl;
	delList(m_list, "劉德華");
	cout << "鏈表長度：" << m_list->clen << endl;
	showList(m_list);

	cout << "---------------------------------------------------" << endl;
	cout << "修改鏈表元素：" << endl;
	updataList(m_list, "張學友", "成龍");
	showList(m_list);

	cout << "---------------------------------------------------" << endl;
	cout << "銷燬鏈表：" << endl;
	destoryList(m_list);

	system("pause");	
	return 0;
}