数据结构——图的链表实现（邻接表表示法）

图的链表实现

之前实现了图的数组实现

http://blog.csdn.net/cinmyheart/article/details/41370465

下图仅作示意性说明，和测试数据有点区别，测试数据还是用的原来数组实现时的测试数据，这并不影响图的数据结构的表示(其实我就是懒得再做一遍原始数据了。。。哈哈)

现对图进行抽象，对于整个图，我用了结构体struct graph,图中有节点，那么节点我用struct vertex 进行抽象，至于struct vertex　adjacent[0]这个技巧是我常用的伎俩

不熟悉或者不知道的话可以看这里

http://blog.csdn.net/cinmyheart/article/details/28985843

这里我想强调一下的就是，权衡了一下，在struct vertex内部我使用了两个指针,一个end 一个next，实质上，看代码就知道，只有头节点会同时用到end和next两个指针，end的存在是为了最快速的跳转指向到链表末尾，然而，除开头节点外，其他节点的end是没有意义的，代码里面其他节点也没有使用end指针。这里是一种权衡考虑，为了最快的跳转到链表末尾，我选择了牺牲一点内存(用来储存end指针的).

/************************************************************
code file	: graph.h
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	This file is a header file for out test program.
We abstract the data structure -- Graph here. And we also
declare some useful API to construct out naive graph :)

************************************************************/

#ifndef _GRAPH_LIST_H
#define _GRAPH_LIST_H

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

	#define CONNECTED    1
	#define DISCONNECTED 0

	#define SUCCESS  0
	#define FAILED  -1

	struct vertex
	{
		int value;
		struct vertex* next;
		struct vertex* end;
	};

	struct graph
	{
		int num_vertex;
		int num_edge;
		struct vertex adjacent[0];
	};

	struct graph* init_graph(int vertex,int edge);
	void   release_graph(struct graph* p_graph);
	
	int add_edge(struct graph* p_graph,char from_v,char to_v);
	int print_graph(struct graph* p_graph);

#endif

对于数据数据结构进行初始化

/************************************************************
code file	: init_graph.c
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	This function is used for initializing the graph
with inputed parameter @vertex and @edge.

************************************************************/
#include "graph_list.h"

struct graph* init_graph(int num_vertex,int num_edge)
{

	if(num_vertex <= 0 || num_edge <= 0)
	{
		return NULL;
	}

	struct graph* p_graph = NULL;

        p_graph = (struct graph*)malloc(sizeof(struct graph) +\
		  num_vertex*sizeof(struct vertex));

	if(!p_graph)
	{
		printf("malloc failed in function %s()\n",__FUNCTION__);
		return NULL;
	}
	
	p_graph->num_vertex = num_vertex;
	p_graph->num_edge   = num_edge;

	int temp = 0;
	//initialize the adjacent relationship
	for(temp = 0;temp < num_vertex;temp++)
	{
		p_graph->adjacent[temp].value = temp;
		p_graph->adjacent[temp].next  = NULL;
		p_graph->adjacent[temp].end   = NULL;
	}
	
	return p_graph;
}

这里开始真正的建立图节点间的链接关系

这里注意到，由于图是双向连同的图，而不是单向的，因此建立A-B关系的时候还要建立B-A关系。

再者，这里我用了三个if　判断语句，细心者会发现，如果前两个条件即使不满足，那么经过前两个if过程的处理，不管怎样，第三个if的条件都为真

而我还是用了if，是为了提醒自己和viewer，当前两个if任意不满足时，进入第三个if内部的时候，adjacent[to/from] .end->next　这个指针实质上是指向此时end本身的,即此时的p_to/from_v,后面会紧跟着有个p_to/from_v->next = NULL,因此不会影响最后节点指向NULL的特性。

/************************************************************
code file	: add_edge.c
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	This function will help us to add a new connection
between different vertex which is in the graph.

*************************************************************/
#include "graph_list.h"

int add_edge(struct graph* p_graph,char from_v,char to_v)
{
	if(!p_graph || from_v < 0 || to_v < 0)
	{
		return FAILED;
	}

	struct vertex* p_to_v    = (struct vertex*)malloc(sizeof(struct vertex));
	struct vertex* p_from_v  = (struct vertex*)malloc(sizeof(struct vertex));

	if(!p_to_v || !p_from_v)
	{
		printf("malloc failed in function %s()\n",__FUNCTION__);

		return FAILED;		
	}


	if(!(p_graph->adjacent[from_v].end))
	{
		p_graph->adjacent[from_v].next  = p_to_v;
		p_graph->adjacent[from_v].end   = p_to_v;
		p_to_v->next  = NULL;
		p_to_v->value = to_v;
	}
	
	if(!(p_graph->adjacent[to_v].end))
	{
		p_graph->adjacent[to_v].next  = p_from_v;
		p_graph->adjacent[to_v].end   = p_from_v;
		p_from_v->next  = NULL;
		p_from_v->value = from_v;
	}
	
	if(p_graph->adjacent[from_v].end && p_graph->adjacent[to_v].end)
	{
		p_graph->adjacent[from_v].end->next = p_to_v;
		p_graph->adjacent[from_v].end       = p_to_v;//update the new end node.
		p_to_v->next  = NULL;
		p_to_v->value = to_v;

		p_graph->adjacent[to_v].end->next = p_from_v;
		p_graph->adjacent[to_v].end       = p_from_v;//update the new end node.
		p_from_v->next  = NULL;
		p_from_v->value = from_v;
		
	}

	return SUCCESS;
}

链表实现时候，图的释放会有点不“优雅”。

节点在内存中离散的分布导致释放时要一个个释放。如果是数组实现的话，一次性就ＯＫ了

/************************************************************
code file	: release_graph.c
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	It's easy and convenient for us to call this API once
and free all the graph.

*************************************************************/
#include "graph_list.h"

void release_graph(struct graph* p_graph)
{
	if(!p_graph)
	{
		return ;
	}
	
	int temp = 0;
	int num_vertex = p_graph->num_vertex;
	struct vertex* p_temp = NULL;

	for(temp = 0;temp < num_vertex;temp++)
	{
		if(p_graph->adjacent[temp].next)
		{
			p_temp = (p_graph->adjacent[temp].next->next);
			while(p_temp)
			{
				free(p_graph->adjacent[temp].next);
				p_graph->adjacent[temp].next = p_temp;
				p_temp = p_temp->next;
			}
			free(p_graph->adjacent[temp].next);
		}
	}

	free(p_graph);
}

打印图节点间的关系

/************************************************************
code file	: print_graph.c
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	This function will print out the connection of graph
which @p_graph point to.

************************************************************/

#include "graph_list.h"

int print_graph(struct graph* p_graph)
{
	if(!p_graph)
	{
		return FAILED;
	}

	int from_v = 0;
	int to_v = 0;

	int num_vertex = p_graph->num_vertex;

	struct vertex* p_vertex = NULL;

	for(from_v = 0;from_v < num_vertex;from_v++)
	{	
		p_vertex = &(p_graph->adjacent[from_v]);
		while(p_vertex)
		{
			printf("\t%d",p_vertex->value);
			p_vertex = p_vertex->next;
		}
		printf("\n");
	}

	return SUCCESS;
}

测试主程序

/****************************************************************
code file	: test_graph.c
code writer	: EOF
code date	: 2014.11.22
e-mail		: jasonleaster@gmail.com

code description:
	Here , we use this program to call some API which would 
construct a ADT--graph and test it.

*****************************************************************/
#include <stdio.h>
#include "graph_list.h"

int main()
{
	struct graph* p_graph = NULL;

	FILE* fp = fopen("./text.txt","r+");

	if(!fp)
	{
		printf("fopen() failed!\n");
		return 0;
	}

	int ret    = 0;
	int vertex = 0;
	int edge   = 0;

	int from_v = 0;
	int to_v   = 0;

	fscanf(fp,"%d",&vertex);
	fscanf(fp,"%d",&edge);

	p_graph = init_graph(vertex,edge);

	int temp = 0;
	for(temp;temp < edge;temp++)
	{
		/*
		**	I think it's necessary to check the returned value
		** of scanf() family.
		*/
		ret = fscanf(fp,"%d %d",&from_v,&to_v);
		if(ret != 2)
		{
			break;
		}

		add_edge(p_graph,from_v,to_v);
	}
	
	print_graph(p_graph);

	release_graph(p_graph);
	fclose(fp);
	return 0;
}

测试文本 text.txt

测试结果：

原文链接：https://blog.csdn.net/u011368821/article/details/41381845

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