hdu1162：Eddy's picture（最小生成树）

http://acm.hdu.edu.cn/showproblem.php?pid=1162

Problem Description

Eddy begins to like painting pictures recently ,he is sure of himself to become a painter.Every day Eddy draws pictures in his small room, and he usually puts out his newest pictures to let his friends appreciate. but the result it can be imagined, the friends are not interested in his picture.Eddy feels very puzzled,in order to change all friends 's view to his technical of painting pictures ,so Eddy creates a problem for the his friends of you.
Problem descriptions as follows: Given you some coordinates pionts on a drawing paper, every point links with the ink with the straight line, causes all points finally to link in the same place. How many distants does your duty discover the shortest length which the ink draws?

Input

The first line contains 0 < n <= 100, the number of point. For each point, a line follows; each following line contains two real numbers indicating the (x,y) coordinates of the point.

Input contains multiple test cases. Process to the end of file.

Output

Your program prints a single real number to two decimal places: the minimum total length of ink lines that can connect all the points.

Sample Input

3
1.0 1.0
2.0 2.0
2.0 4.0

Sample Output

3.41

题意分析：

给出n个点，求把这些点连接起来的最小长度。

Prim算法：

#include <stdio.h>
#include <string.h> 
#include <math.h>
#define N 120
double e[N][N], dis[N];
int book[N];
struct data{ 
	double x;
	double y;
}a[N];
int main()
{
	int n, i, j,  u, v, count, inf=99999999;
	double mini, sum;
	while(scanf("%d", &n)!=EOF)
	{
		for(i=1; i<=n; i++)
			for(j=1; j<=n; j++)
				if(i==j)
					e[i][j]=0;
				else
					e[i][j]=inf;
		for(i=1; i<=n; i++)
		{
			scanf("%lf %lf", &a[i].x, &a[i].y);
			for(j=1; j<=n; j++)
				e[i][j]=e[j][i]=sqrt((a[i].x-a[j].x)*(a[i].x-a[j].x) + (a[i].y-a[j].y)*(a[i].y-a[j].y));
		}
		for(i=1; i<=n; i++)
			dis[i]=e[1][i];
		memset(book, 0, sizeof(book));
		book[1]=1;
		sum=0;
		count=1;
		while(count<n)
		{
			mini=inf;
			for(i=1; i<=n; i++)	
			{
				if(book[i]==0 && dis[i]<mini)
				{
					mini=dis[i];
					u=i;
				}
			}
			sum+=dis[u];
			book[u]=1;
			count++;
			for(v=1; v<=n; v++)
				if(!book[v] && e[u][v]<dis[v])
					dis[v]=e[u][v];
		}
		printf("%.2lf
", sum);	
	}
	return 0;
}

Kruskal算法：

#include <stdio.h>
#include <string.h> 
#include <math.h>
#include <algorithm>
using namespace std;
#define N 120
int f[N];
struct data{ 
	double x;
	double y;
}a[N];
struct cou{
	int u;
	int v;
	double l;
}e[N*N];
int cmp(cou a, cou b)
{
	return a.l<b.l;
}
int getf(int v)
{
	if(f[v]==v)
		return v;
	else
	{
		f[v]=getf(f[v]);
		return f[v];
	}
}
int merge(int u, int v)
{
	int t1, t2;
	t1=getf(u);
	t2=getf(v);
	if(t1!=t2)
	{
		f[t2]=t1;
		return 1;
	}
	return 0;
}
int main()
{
	int n, i, j, t, count, inf=99999999;
	double mini, sum;
	while(scanf("%d", &n)!=EOF)
	{
		count=0;
		for(i=1; i<=n; i++)
		{
			scanf("%lf %lf", &a[i].x, &a[i].y);
			for(j=1; j<i; j++)
			{
				e[count].u=i;
				e[count].v=j;
				e[count].l=sqrt((a[i].x-a[j].x)*(a[i].x-a[j].x) + (a[i].y-a[j].y)*(a[i].y-a[j].y));
				count++;
			}	
		}
		sort(e, e+count, cmp);
		for(i=1; i<=n; i++)
			f[i]=i;
		t=0;
		sum=0;
		for(i=0; i<count; i++)
		{
			if(merge(e[i].u, e[i].v))
			{
				t++;
				sum+=e[i].l;
			}
			if(t==n-1)
				break;
		}
		printf("%.2lf
", sum);
	}
	return 0;
}