HDU 1857 （prim+平面坐标+题意理解）

汉语题：http://acm.hdu.edu.cn/showproblem.php?pid=1875

题意很容易想多。其实直接暴力。发现了一个存在独立边判断情况。在prim中加一个flag。

#include<cstdio>
#include<cstring>
#include<cmath>

class Node
{
public:
    double x,y;
}edge[110];

double gragh[110][110];;
double dis[110];
int n,visit[110];
double ans;

double distance(double x1,double y1,double x2,double y2)
{
    double dx = x1 - x2;
    double dy = y1 - y2;
    return sqrt(dx*dx+dy*dy);
}

int prim()
{
    for(int i = 1;i <= n; i++)
        dis[i] = gragh[1][i];
    memset(visit,0,sizeof(visit));
    for(int i = 1;i < n; i++){
        double Min = 99999999;
        int pos,flag = true;
        for(int j = 2;j<= n; j++){
            if(visit[j] == 0 && dis[j] < Min){
                Min = dis[j];
                pos = j;
                flag = false;
            }
        }
        if(flag)
            return 0;
        visit[pos] = true;
        for(int j = 1;j <= n; j++){
            if(visit[j] == 0 && dis[j] > gragh[pos][j])
                dis[j] = gragh[pos][j];
        }
    }
    for(int i = 2;i <= n; i++)
        if(dis[i] == 99999999)
            return 0;
        else
            ans += dis[i];
    return 1;
}

int main()
{
    //freopen("in.txt","r",stdin);
    int ncase;
    scanf("%d",&ncase);
    while(ncase--){
        scanf("%d",&n);
        for(int i = 1;i <= n; i++)
            scanf("%lf%lf",&edge[i].x,&edge[i].y);
        for(int i = 1;i <= n; i++){
            for(int j = 1;j <= n; j++){
                double d = distance(edge[i].x,edge[i].y,edge[j].x,edge[j].y);
                if(d >= 10 && d <= 1000)
                    gragh[i][j] = gragh[j][i] = d;
                else
                    gragh[i][j] = gragh[j][i] = 99999999;
            }
        }
        ans = 0;
        if(prim())
            printf("%.1f\n",ans*100);
        else
            printf("oh!\n");
    }
    return 0;
}