hdu1162 Eddy's picture (prim最小生成树)

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
#define INF 1000000.0
#define MAXN 102
using namespace std;
//最小生成树
double map[MAXN][MAXN],dist[MAXN];
double px[MAXN],py[MAXN];
int visited[MAXN];

double distans(double x1,double x2,double y1,double y2)
{
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

double prim(int n)
{
	int i,j,u;
	double min,sum=0.0;
	for (i=1;i<=n;i++)
	{
		dist[i]=map[1][i];
		visited[i]=0;
	}
	visited[1]=1;
	dist[1]=0.0;
	for (i=2;i<=n;i++)
	{
		min=INF;
		u=1;
		for(j=1;j<=n;j++)
			if(!visited[j]&&dist[j]<min)
			{
				min=dist[j];
				u=j;
			}
		visited[u]=1;
		sum+=min;
		for(j=1;j<=n;j++)
			if(!visited[j]&&dist[j]>map[u][j])
				dist[j]=map[u][j];
	}
	return sum;
}

int main()
{
	int n,i,j;
	double ans;
	while(scanf("%d",&n)!=EOF)
	{
		for(i=1;i<=n;i++)
			scanf("%lf %lf",&px[i],&py[i]);
		for (i=1;i<=n;i++)
		{
			for (j=i;j<=n;j++)
			{
				map[i][j]=map[j][i]=distans(px[i],px[j],py[i],py[j]);
			}
		}
		ans=prim(n);
		printf("%.2lf\n",ans);
	}
	return 0;
}

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