hdu 1162 Eddy's picture

这是一道=最小生成树的问题，我用的是prim算法解决的

#include<stdio.h>
#include<math.h>
#include<string.h>
#define maxn 105
struct point 
{
	double x,y;
}p[maxn];
double cost[maxn][maxn];
double dis(point a, point b)
{
	return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
#define typec double 
const typec inf=0x3f3f3f3f;
int vis[maxn];
double low[maxn];
double prim(double cost[][maxn],int n)
{
	int i,j,p;
	double min,res=0;
	memset(vis,0,sizeof(vis));
	vis[0]=1;
	for(i=1;i<n;i++)
	{
		low[i]=cost[0][i];
	}
	for(i=1;i<n;i++)
	{
		min=inf;
		p=-1;
		for(j=0;j<n;j++)
			if(!vis[j]&&min>low[j])
			{
				min=low[j];
				p=j;
			}
		if(min==inf)
			return -1;
		res+=min;
		vis[p]=1;
		for(j=0;j<n;j++)
			if(!vis[j]&&low[j]>cost[p][j])
			{
				low[j]=cost[p][j];
			}
	}
	return res;
}
int main()
{
	int n;
	while(~scanf("%d",&n))
	{
		for(int i=0;i<n;i++)
			scanf("%lf%lf",&p[i].x,&p[i].y);
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<n;j++)
			{
				if(i==j)
				{
					cost[i][j]=0;
				}
				else
					cost[i][j]=dis(p[i],p[j]);
			}
		}
		printf("%.2f\n",prim(cost,n));
	}
	return 0;
}