HDU 1162 (最小生成树)

#include <cstdio>
#include <cstring>
#include <cmath>
#define INF 0xfffffff
double map[102][102],lowcost[102];
bool visited[102];
struct Point {
	double x,y;
}point[102];
double distance (Point a,Point b){
	return sqrt ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
//----普利姆算法
double Prim (int n){
	int k;
	memset (visited,0,sizeof (visited));
	visited[1] = true;
	double tmp,sum=0;
	for (int i=1;i<=n;i++)
		lowcost[i] = map[1][i];
	for (int i=2;i<=n;i++){
		tmp = INF;
		for (int j=1;j<=n;j++)
			if (!visited[j] && lowcost[j] < tmp)
				tmp = lowcost[k=j];
	//	printf ("tmp=%.2lf\n",tmp);
		if (tmp == INF) break;
		visited[k] = true;
		sum += tmp;
		for (int i=1;i<=n;i++)
			if (!visited[i] && map[k][i] < lowcost[i])
				lowcost[i] = map[k][i];
	}
	return sum;
}
int main (){
#ifndef ONLINE_JUDGE
	freopen ("in.txt","r",stdin);
#endif
	int n;
	while (~scanf ("%d",&n)){
		//----初始化map
		for (int i=1;i<=n;i++)
			for (int j=1;j<=n;j++)
			map[i][j] = INF;
		//----输入坐标点
		for (int i=1;i<=n;i++)
			scanf ("%lf%lf",&point[i].x,&point[i].y);
		//---------输出任意两点之间的距离---------
		for (int i=1;i<n;i++)
			for (int j=i+1;j<=n;j++){
				double tmp = distance (point[i],point[j]);
			//	printf ("dis==%.2lf\n",tmp);
				map[i][j] = tmp;    //---错误1.得到了 i 到 j 的距离，没有给出 j 到 i 的距离。实际是：map[i][j] = map[j][i] = tmp;
			}
		printf ("%.2lf\n",Prim(n));
	}
	return 0;
}

#include <cstdio>
#include <cstring>
#include <cmath>
#define INF 0xfffffff
double map[102][102],lowcost[102];
bool visited[102];
struct Point {
	double x,y;
}point[102];
double distance (Point a,Point b){
	return sqrt ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
//----普利姆算法
double Prim (int n){
	int k;
	memset (visited,0,sizeof (visited));
	visited[1] = true;
	double tmp,sum=0;
	for (int i=1;i<=n;i++)
		lowcost[i] = map[1][i];
	for (int i=2;i<=n;i++){
		tmp = INF;
		for (int j=1;j<=n;j++)
			if (!visited[j] && lowcost[j] < tmp)
				tmp = lowcost[k=j];
	//	printf ("tmp=%.2lf\n",tmp);
		if (tmp == INF) break;
		visited[k] = true;
		sum += tmp;
		for (int i=1;i<=n;i++)
			if (!visited[i] && map[k][i] < lowcost[i])
				lowcost[i] = map[k][i];
	}
	return sum;
}
int main (){
#ifndef ONLINE_JUDGE
	freopen ("in.txt","r",stdin);
#endif
	int n;
	while (~scanf ("%d",&n)){
		//----初始化map
		for (int i=1;i<=n;i++)
			for (int j=1;j<=n;j++)
			map[i][j] = INF;
		//----输入坐标点
		for (int i=1;i<=n;i++)
			scanf ("%lf%lf",&point[i].x,&point[i].y);
		//---------输出任意两点之间的距离---------
		for (int i=1;i<n;i++)
			for (int j=i+1;j<=n;j++){
				double tmp = distance (point[i],point[j]);
			//	printf ("dis==%.2lf\n",tmp);
				map[i][j] = map[j][i] = tmp;
			}
		printf ("%.2lf\n",Prim(n));
	}
	return 0;
}