Union Find

动态链接:

              这里union(x,y) 相当于一个函数，这个函数建立两个点，x，y的链接。而connected(x,y)用于检测两点的链接性，即是否处于链接状态.

connected(0,7)就是用于检测0,7这两点是否相连。

Union find能做很酷帅的事情，迷宫连通图的查找~

对链接性进行建模

把“链接” 等效为三种形式:

自身式: P 链接向P

双向式: P链接向Q，Q链接向P

传递式：P链接向Q，Q链接向R，于是我们说P链接向R

Union-find data type (API)

void union(int p, int q)
boolean connected(int p, int q)

感觉这个API设计的还是不够合理（个人观点），仅仅靠输入的p，q是无法对所有元素操作的，意味着这里函数要额外的获取一个全局变量去多所有元素进行操作。而这对于函数的封装性是不好的.

函数应该尽可能少的去依赖除了入口参数以外的数据.当外部全局变量发生变化时不至于影响函数内部(函数内部如果没有依赖外部的全局变量的话)，从而提高函数的健壮性.

于是 API的入口更改如下:

void union_element(int* p_array,int size,int p, int q);
int  connected_element(int* p_array,int size,int p,int q);

这里给出自己的C 语言实现

/*********************************************************
code writer	: EOF
code date	: 2014.09.07
code file 	: union_find.c
e-mail		: jasonleaster@gmail.com

code purpose	:
	A demo for union-find.

	If there is something wrong with my code, please
touch me by e-mail. Thank you. :-)

**********************************************************/
#include <stdio.h>
#include <malloc.h>

#define SAME 1
#define DIFF 0

#define DEBUG

//----------------------------------------------------
void union_element(int* p_array,int size,int p, int q);
int  connected_element(int* p_array,int size,int p,int q);
//----------------------------------------------------

int init_element(int* p_array,int size);

int main()
{
	int num = 0;
	int ret = 0;
	int* all_element = NULL;

	printf("Please input how many number in your union group\n");	

	while(!scanf("%d",&num))
	{
		getchar();
		printf("scanf error, please input again\n");
	}

	all_element = (int*)malloc(sizeof(int) * num);
	
	init_element(all_element,num);
	/*
	**	It's time to test our API
	*/

#ifdef DEBUG
	union_element(all_element,num,4,3);
	union_element(all_element,num,3,8);
	union_element(all_element,num,6,5);
	union_element(all_element,num,9,4);
	union_element(all_element,num,2,1);

	ret = connect_element(all_element,num,0,7);

	if(ret == SAME)
	{
		printf("Y Connected!\n");
	}
	else if (ret == DIFF)
	{
		printf("X Unconnected!\n");
	}

	ret = connect_element(all_element,num,8,9);
	if(ret == SAME)
	{
		printf("Y Connected!\n");
	}
	else if (ret == DIFF)
	{
		printf("X Unconnected!\n");
	}
#endif
	free(all_element);
	all_element = NULL;
	return 0;
}

void union_element(int* p_array,int size,int p, int q)
{
	if(!p_array)
	{
		printf("function:%s line: %d p_array is NULL\n",__FUNCTION__,__LINE__);
		return ;
	}

	if(p > (size-1) || q > (size-1))
	{
		printf("index 'p' 'q' are bigger than the max size of array\n");
		printf("p: %3d q: %3d",p,q);
		return ;
	}

	int p_union = p_array[p];
	int q_union = p_array[q];

	int tmp = 0;
	
	for(tmp = 0; tmp < size ;tmp++)
	{
		if(p_array[tmp] == p_union)
		{
			p_array[tmp] = q_union;
		}
	}
}

int connect_element(int* p_array,int size,int p ,int q)
{
	if(!p_array)
	{
		printf("function:%s line: %d p_array is NULL\n",__FUNCTION__,__LINE__);
		return -1;
	}

	if(p > (size-1) || q > (size-1))
	{
		printf("index 'p' 'q' are bigger than the max size of array\n");
		printf("p: %3d q: %3d",p,q);
		return ;
	}

	if(p_array[p] == p_array[q])
	{
		return SAME;
	}
	else
	{
		return DIFF;
	}
}

int init_element(int* p_array,int size)
{
	if(!p_array)
	{
		printf("p_array is NULL!\nNeedless to initialize\n");
		return -1;
	}

	int tmp = 0;

	for(tmp = 0; tmp < size; tmp++)
	{
		p_array[tmp] = tmp;
	}
}

Union Find