数据结构(C语言版)第四章:链表

4.1 指针

实际上并不推荐使用malloc和free,使用malloc还简单,但是当指针进行移动的时候,你如何确定在哪个地址上free内存,则是个大难题.

我们写个正常的malloc和free程序:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( void )
{
	int *pi = ( int * )malloc( sizeof( int ) );
	*pi = 4;
	printf("%d\n", *pi );
	free( pi );

	return 0;
}

然后写个比较怪怪的函数:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( void )
{
	char **pstr = ( char ** )malloc( sizeof( char ) * 100 );
	*pstr = "hello world";
	printf("%s\n", *pstr );
	free( pstr );

	return 0;
}

这段代码至少对目前的我来说,有点怪异(虽然是我自己写出来的).写这段代码有以下的含义:

1. 对于char *,最好理解为字符串,而不是字符指针(虽然操作的时候,可以通过字符指针进行操作)

2. 对于malloc函数,要分配确定的大小,所以程序中为sizeof(char)而不是sizeof(char*),因为指针在特定的机子上的大小不同(一般为4字节)

3. 在free中,一定要找对free的起始地址.比如我如果这样修改,则会报错:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( void )
{
	char **pstr = ( char ** )malloc( sizeof( char ) * 100 );
	*pstr = "hello world";
	printf("%c---%s---%p\n", **pstr, *pstr, pstr );
	pstr++;

	free( pstr );

	return 0;
}

程序很恐怖的输出:

你能确保在编写代码中,用到free的时候,不会一不小心的移动了一下指针??至少我基本不敢用free,也是这个原因.这也导致了实际上我也不太敢用malloc.

4.2 链表

简单写一个单链表,数据元素为字符串,支持增加,删除,查找.按字符串的字典顺序排序.

PS:实际上这里的难度在于:C语言只能传值,所以你必须传递指针的指针到函数中去.而传递指针的指针也很麻烦,那么我们可以这样想:用一个固定的节点当作头指针,而实际的头节点当作第二个指针即可:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct LINK{
	char				*word;
	struct LINK		*next;
}Link;

void insert( Link *link, char *word )
{
	Link *temp = ( Link * )malloc( sizeof( Link ) );	//用于存储新的值
	Link *tempLink = ( Link * )malloc( sizeof( Link ) );	//在插入节点时存储上一个节点
	temp->word = word;
	temp->next = NULL;
	if ( NULL == link->next ){
		link->next = temp;
	}
	else{
		tempLink = link;				//存储上一个节点
		link = link->next;
		while ( NULL != link ){
			if ( -1 == strcmp( link->word, word ) ){
				tempLink = link;
				link = link->next;
			}
			else if ( 0 == strcmp( link->word, word ) ){
				return;
			}
			else{
				temp->next = link;
				tempLink->next = temp;
				return;
			}
		}
		if ( NULL == link ){					//判断为尾节点的特殊情况
			tempLink->next = temp;
		}
	}
}

int delete( Link *link, char *word )
{
	Link *tempLink = ( Link * )malloc( sizeof( Link ) );		//用于存储删除元素的上一个节点
	tempLink = link;
	link = link->next;
	while ( NULL != link ){
		if ( 0 != strcmp( link->word, word ) ){
			tempLink = link;
			link = link->next;
		}
		else{
			tempLink->next = link->next;
			return 1;
		}
	}

	return 0;
}

void show( Link *link ){
	while ( NULL != link ){
		printf("%s-->", link->word );
		link = link->next;
	}

	printf("NULL\n");
}

int main( void )
{
	Link *link = ( Link * )malloc( sizeof( Link ) );
	link->next = NULL;
	link->word = "EOF";		//这里假定没有字符串等于EOF
	insert( link, "cc" );
	insert( link, "dd" );
	insert( link, "aa" );
	insert( link, "bb" );
	insert( link, "ba" );
	insert( link, "cb" );

	show( link->next );

	delete( link, "bb" );
	delete( link, "dd" );
	delete( link, "ff" );

	show( link->next );

	return 0;
}

程序输出:

有道题比较难(真的写的时候也不难,只是之前我没写出来,现在写出来罢了),就是将链表进行翻转,但不能借助其他的存储空间(如果能的话,相当于对delete一个链表再insert成一个链表),代码如下:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct LINK{
	char				*word;
	struct LINK		*next;
}Link;

void insert( Link *link, char *word )
{
	Link *temp = ( Link * )malloc( sizeof( Link ) );	//用于存储新的值
	Link *tempLink = ( Link * )malloc( sizeof( Link ) );	//在插入节点时存储上一个节点
	temp->word = word;
	temp->next = NULL;
	if ( NULL == link->next ){
		link->next = temp;
	}
	else{
		tempLink = link;				//存储上一个节点
		link = link->next;
		while ( NULL != link ){
			if ( -1 == strcmp( link->word, word ) ){
				tempLink = link;
				link = link->next;
			}
			else if ( 0 == strcmp( link->word, word ) ){
				return;
			}
			else{
				temp->next = link;
				tempLink->next = temp;
				return;
			}
		}
		if ( NULL == link ){					//判断为尾节点的特殊情况
			tempLink->next = temp;
		}
	}
}

int delete( Link *link, char *word )
{
	Link *tempLink = ( Link * )malloc( sizeof( Link ) );		//用于存储删除元素的上一个节点
	tempLink = link;
	link = link->next;
	while ( NULL != link ){
		if ( 0 != strcmp( link->word, word ) ){
			tempLink = link;
			link = link->next;
		}
		else{
			tempLink->next = link->next;
			return 1;
		}
	}

	return 0;
}

void show( Link *link ){
	while ( NULL != link ){
		printf("%s-->", link->word );
		link = link->next;
	}

	printf("NULL\n");
}

void reverse( Link *link )
{
	Link *tail = ( Link * )malloc( sizeof( Link ) );
	Link *mid = ( Link * )malloc( sizeof( Link ) );
	Link *prev = ( Link * )malloc( sizeof( Link ) );
	Link *head = ( Link * )malloc( sizeof( Link ) );
	head = link;
	tail = NULL;
	link = link->next;
	if ( NULL != link ){
		mid = link;
		prev = link->next;
		while ( NULL != prev ){
			mid->next = tail;
			tail = mid;
			mid = prev;
			prev = prev->next;
		}
		mid->next = tail;
		head->next = mid;
	}
}

int main( void )
{
	Link *link = ( Link * )malloc( sizeof( Link ) );
	link->next = NULL;
	link->word = "EOF";		//这里假定没有字符串等于EOF
	insert( link, "cc" );
	insert( link, "dd" );
	insert( link, "aa" );
	insert( link, "bb" );
	insert( link, "ba" );
	insert( link, "cb" );

	show( link->next );

	delete( link, "bb" );
	delete( link, "dd" );
	delete( link, "ff" );

	show( link->next );

	reverse( link );
	show( link->next );

	return 0;
}

程序输出:

4.3 动态链栈与动态链队列

动态链栈与动态链队列没什么特别的地方,主要就是多个链栈的集合而已,而传递的时候只要把每个栈的地址传递到函数里面去就可以了.

4.4 多项式

多项式的相加:书上的方法很牛,它是直接返回一个地址的.效率在我看来,是所有多项式相加里面最高的.但是我个人感觉,代码应该简洁,更应该有良好的阅读感.所以我打算是将相加的结果当作一个指针传递进去,而不是从函数内返回回来:

先把自己写的错误的代码粘贴出来,用于铭记(对待C,C++,都要用及其认真的态度来对待):

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct POLYNODE{
	int							coef;
	int							expon;
	struct POLYNODE	*next;
}PolyNode;

void padd( PolyNode *exp1, PolyNode *exp2, PolyNode *exp )
{
	PolyNode *addNode;

	while ( exp1 && exp2 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		if ( exp1->expon < exp2->expon ){
			addNode->coef = exp2->coef;
			addNode->expon = exp2->expon;
			addNode->next = NULL;
			exp = addNode;
			exp = exp->next;
			exp2 = exp2->next;
			continue;
		}
		else if ( exp1->expon == exp2->expon ){
			if ( 0 == ( exp1->coef + exp2->coef ) ){
				exp1 = exp1->next;
				exp2 = exp2->next;
				continue;
			}
			addNode->coef = exp1->coef + exp2->coef;
			addNode->expon =  exp1->expon;
			addNode->next = NULL;
			exp = addNode;
			exp = exp->next;
			exp1 = exp1->next;
			exp2 = exp2->next;
			continue;
		}
		else{
			addNode->coef = exp1->coef;
			addNode->expon = exp1->expon;
			addNode->next = NULL;
			exp = addNode;
			exp = exp->next;
			exp1 = exp1->next;
			continue;
		}
	}

	while ( exp1 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		addNode->coef = exp1->coef;
		addNode->expon = exp1->expon;
		addNode->next = NULL;
		exp = addNode;
		exp = exp->next;
		exp1 = exp1->next;
	}

	while ( exp2 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		addNode->coef = exp2->coef;
		addNode->expon = exp2->expon;
		addNode->next = NULL;
		exp = addNode;
		exp = exp->next;
		exp2 = exp2->next;
	}
}

void show( PolyNode *exp )
{
	exp = exp->next;
	while ( exp ){
		printf("%d * x^%d + ", exp->coef, exp->expon );
		exp = exp->next;
	}
	printf("0\n");
}

int main( void )
{
	PolyNode *exp1 = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode *exp2 = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode *exp = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode node1_1, node1_2, node1_3, node2_1, node2_2, node2_3;
	exp1->next = NULL;
	exp2->next = NULL;
	exp->next = NULL;

	node1_1.coef = 3;
	node1_1.expon = 14;
	node1_1.next = &node1_2;
	node1_2.coef = 2;
	node1_2.expon = 8;
	node1_2.next = &node1_3;
	node1_3.coef = 1;
	node1_3.expon = 0;
	node1_3.next = NULL;

	node2_1.coef = 8;
	node2_1.expon = 14;
	node2_1.next = &node2_2;
	node2_2.coef = -3;
	node2_2.expon = 10;
	node2_2.next = &node2_3;
	node2_3.coef = 10;
	node2_3.expon = 6;
	node2_3.next = NULL;

	exp1->next = &node1_1;
	exp2->next = &node2_1;

	padd( exp1->next, exp2->next, exp->next );

	show( exp );

	return 0;
}

之前写的错误有以下:

1. 一定要把头指针传递进去:

padd( exp1, exp2, exp );

但是,如果exp1,exp2只是用来读取而不进行修改,可以传递exp1->next进去.

2. 对链表的插入,不能这样操作:

exp = addNode;
exp = exp->next;

在头部可以这样插入,但是在尾部@_@,sorry,空指针会不断的把exp初始化为NULL.

所以代码修改如下(模块化):

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct POLYNODE{
	int							coef;
	int							expon;
	struct POLYNODE	*next;
}PolyNode;

void insert( PolyNode *exp, PolyNode *addNode )
{
	if ( NULL == exp->next ){
		exp->next = addNode;
	}
	else{
		exp = exp->next;
		while ( NULL != exp->next ){
			exp = exp->next;
		}
		exp->next = addNode;
	}
}
void padd( PolyNode *exp1, PolyNode *exp2, PolyNode *exp )
{
	PolyNode *addNode;

	while ( exp1 && exp2 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		if ( exp1->expon < exp2->expon ){
			addNode->coef = exp2->coef;
			addNode->expon = exp2->expon;
			addNode->next = NULL;
			insert( exp, addNode );
			exp2 = exp2->next;
			continue;
		}
		else if ( exp1->expon == exp2->expon ){
			if ( 0 == ( exp1->coef + exp2->coef ) ){
				exp1 = exp1->next;
				exp2 = exp2->next;
				continue;
			}
			addNode->coef = exp1->coef + exp2->coef;
			addNode->expon =  exp1->expon;
			addNode->next = NULL;
			insert( exp, addNode );
			
			exp1 = exp1->next;
			exp2 = exp2->next;
			continue;
		}
		else{
			addNode->coef = exp1->coef;
			addNode->expon = exp1->expon;
			addNode->next = NULL;
			insert( exp, addNode );
			
			exp1 = exp1->next;
			continue;
		}
	}

	while ( exp1 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		addNode->coef = exp1->coef;
		addNode->expon = exp1->expon;
		addNode->next = NULL;
		insert( exp, addNode );
		
		exp1 = exp1->next;
	}

	while ( exp2 ){
		addNode = ( PolyNode * )malloc( sizeof( PolyNode ) );
		addNode->coef = exp2->coef;
		addNode->expon = exp2->expon;
		addNode->next = NULL;
		insert( exp, addNode );
		
		exp2 = exp2->next;
	}
}

void show( PolyNode *exp )
{
	exp = exp->next;
	while ( exp ){
		printf("%d * x^%d + ", exp->coef, exp->expon );
		exp = exp->next;
	}
	printf("0\n");
}

int main( void )
{
	PolyNode *exp1 = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode *exp2 = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode *exp = ( PolyNode * )malloc( sizeof( PolyNode ) );
	PolyNode node1_1, node1_2, node1_3, node2_1, node2_2, node2_3;
	exp1->next = NULL;
	exp2->next = NULL;
	exp->next = NULL;

	node1_1.coef = 3;
	node1_1.expon = 14;
	node1_1.next = &node1_2;
	node1_2.coef = 2;
	node1_2.expon = 8;
	node1_2.next = &node1_3;
	node1_3.coef = 1;
	node1_3.expon = 0;
	node1_3.next = NULL;

	node2_1.coef = 8;
	node2_1.expon = 14;
	node2_1.next = &node2_2;
	node2_2.coef = -3;
	node2_2.expon = 10;
	node2_2.next = &node2_3;
	node2_3.coef = 10;
	node2_3.expon = 6;
	node2_3.next = NULL;

	exp1->next = &node1_1;
	exp2->next = &node2_1;

	padd( exp1->next, exp2->next, exp );

	show( exp );

	return 0;
}

程序输出:

多项式的循环链表中,涉及到一个非常有用的概念:内存池.就是分配一块内存用于存储和删除,这样就不必每次malloc了.但是这里内存池实际上可以用数组来实现(堆栈),这样更加的方便.于是自己写了以下的算法:

PS:这里为了简单的讨论,链表的插入就直接在头部插入了,而且并不是循环链表:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_STACK 100

typedef struct NODE{
	int					data;
	struct NODE	*next;
}Node;

Node stack[ MAX_STACK ];
int top = 0;

void insert( Node *node, int data )
{
	Node *tempnode;
	if ( top == MAX_STACK - 1 ){
		printf("sorry. 木有内存空间了\n");
		return;
	}
	tempnode = &stack[ top++ ];		//这样做只是为了top能及时的++
	tempnode->data = data;
	tempnode->next = NULL;
	if ( NULL == node->next ){
		node->next = tempnode;
	}
	else{
		tempnode->next = node->next;
		node->next = tempnode;
	}
}

void show( Node *node )
{
	node = node->next;
	while ( node ){
		printf("%d->", node->data );
		node = node->next;
	}
	printf("NULL\n");
}

int main( void )
{
	Node node = stack[ top++ ];
	node.next = NULL;
	insert( &node, 1 );
	insert( &node, 2 );
	insert( &node, 3 );
	insert( &node, 4 );
	insert( &node, 5 );

	show( &node );

	return 0;
}

程序输出:

如果你手贱的话,可能会写出下列的代码(我的第一版本---结果调试的时候发现指针乱窜):

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_STACK 100

typedef struct NODE{
	int					data;
	struct NODE	*next;
}Node;

Node stack[ MAX_STACK ];
int top = 0;

void insert( Node *node, int data )
{
	Node tempnode;
	if ( top == MAX_STACK - 1 ){
		printf("sorry. 木有内存空间了\n");
		return;
	}
	tempnode = stack[ top++ ];		//这样做只是为了top能及时的++
	tempnode.data = data;
	tempnode.next = NULL;
	if ( NULL == node->next ){
		node->next = &tempnode;
	}
	else{
		tempnode.next = node->next;
		node->next = &tempnode;
	}
}

void show( Node *node )
{
	node = node->next;
	while ( node ){
		printf("%d->", node->data );
		node = node->next;
	}
	printf("NULL\n");
}

int main( void )
{
	Node node = stack[ top++ ];
	node.next = NULL;
	insert( &node, 1 );
	insert( &node, 2 );
	insert( &node, 3 );
	insert( &node, 4 );
	insert( &node, 5 );

	show( &node );

	return 0;
}

你会发现tempnode的地址实际上会指向之前赋值的node,然后tempnode不断的被更改,就是实际上:

tempnode = stack[ top++ ];

并没有达到你想要的效果.

4.5 链表的其他操作

1. 翻转单链表---在上面已经写过了.

2. 串接单链表---把第二个链表的头节点放在第一个链表的尾节点即可.

4.6 等价关系

关于等价关系,我并不了解书上的那个VLSI的应用场景,所以略过.

4.7 稀疏矩阵

书上用稀疏矩阵的数据结构过于麻烦,直接不想看.在编程的世界里,有几点必须注意:1. 尽量把代码写简单.2.性能没有你想象中的那么重要,可维护性在某些方面更加重要.所以,在做项目的时候,如果性能没有那么重要,推荐使用高级语言,不要使用C.C只是用来打基础的.

4.8 双向链表

最后以一个双向链表的实现来结束本章(这里只是简单的实现,并没有设计到排序等情况.链表的作用是用于存储,如果关联到排序,请使用二叉树.这里要用循环链表实现,否则你得维护两张链表):

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct DLINK{
	int						data;
	struct DLINK		*prev;
	struct DLINK		*next;
}Dlink;

void insertFront( Dlink *dlink, int data );
void insertTail( Dlink *dlink, int data );
void delete( Dlink *dlink, int data );
int search( Dlink *dlink, int data );
void show( Dlink *dlink );

int main( void )
{
	int i = 0;
	Dlink *dlinkHead = ( Dlink * )malloc( sizeof( Dlink ) );
	dlinkHead->next = dlinkHead->prev = NULL;

	for ( i = 0; i < 10; i++ ){
		insertFront( dlinkHead, i );
		insertTail( dlinkHead, i );
	}

	for ( i = 0; i < 10; i += 3 ){
		delete( dlinkHead, i );
	}

	if ( search( dlinkHead, 5 ) ){
		printf("5 in the double link list\n");
	}
	else{
		printf("5 not in the double link list\n");
	}

	if ( search( dlinkHead, 3 ) ){
		printf("3 in the double link list\n");
	}
	else{
		printf("3 not in the double link list\n");
	}

	show( dlinkHead );

	return 0;
}

void insertFront( Dlink *dlink, int data )
{
	Dlink *tempDlink = ( Dlink * )malloc( sizeof( Dlink ) );
	tempDlink->data = data;
	if ( ( NULL == dlink->prev ) && ( NULL == dlink->next ) ){
		dlink->prev = tempDlink;
		dlink->next = tempDlink;
	}
	else{
		dlink->next->prev = tempDlink;
		tempDlink->prev = NULL;			//用于判断链表的头部
		tempDlink->next = dlink->next;
		dlink->next = tempDlink;
	}
}

void insertTail( Dlink *dlink, int data )
{
	Dlink *tempDlink = ( Dlink * )malloc( sizeof( Dlink ) );
	tempDlink->data = data;
	if ( ( NULL == dlink->prev ) && ( NULL == dlink->next ) ){
		dlink->prev = tempDlink;
		dlink->next = tempDlink;
	}
	else{
		tempDlink->prev = dlink->prev;
		tempDlink->next = NULL;			//用于判断链表的尾部
		dlink->prev->next = tempDlink;
		dlink->prev = tempDlink;
	}
}

void delete( Dlink *dlink, int data )
{
	Dlink *headNode = ( Dlink * )malloc( sizeof( Dlink ) );
	headNode = dlink;		//用于存储头节点
	if ( ( NULL == dlink->prev ) && ( NULL == dlink->next ) ){
		return;
	}
	dlink = dlink->next;
	while ( dlink->next ){
		if ( data != dlink->data ){
			dlink = dlink->next;
		}
		else{
			if ( NULL == dlink->prev ){
				headNode->next = dlink->next;
				dlink->prev = NULL;
			}
			else if ( NULL == dlink->next ){
				headNode->prev = dlink->prev;
				dlink->prev->next = NULL;
			}
			else{
				dlink->next->prev = dlink->prev;
				dlink->prev->next = dlink->next;
			}
			dlink = dlink->next;
		}
	}
}
int search( Dlink *dlink, int data )
{
	dlink = dlink->next;
	while ( dlink ){
		if ( data == dlink->data ){
			return 1;
		}
		dlink = dlink->next;
	}

	return 0;
}
void show( Dlink *dlink )
{
	dlink = dlink->next;

	while ( dlink ){
		printf("%d-->", dlink->data );
		dlink = dlink->next;
	}

	printf("NULL\n");
}

程序输出:

来源：oschina

链接：https://my.oschina.net/u/1017135/blog/182196