HDU 2122

思路：prime，考虑重边！！！

#include<stdio.h>
#include<string.h>
int map[1001][1001],dist[1001];
int vis[1001],n;
void init1()
{
    int i,j;
    for(i = 0;i < n;i ++)
    {
        for(j = 0;j < n;j ++)
        {
            if(i != j)
                map[i][j] = 1 << 30;
        }
    }
}
void init2()
{
    int i;
    memset(vis,0,sizeof(vis));
    for(i = 0;i < n;i ++)
        dist[i] = map[0][i];
}
int main()
{
    int m,i,j,k,cnt;
    int min,len,sum,a,b;
    while(~scanf("%d%d",&n,&m))
    {
        init1();
        sum = cnt = 0;
        while(m--)
        {
            scanf("%d%d%d",&a,&b,&len);
            if(len < map[a][b])
                map[a][b] = map[b][a] = len;
        }
        init2();
        vis[0] = 1;
        for(i = 0;i < n;i ++)
        {
            min = 1 << 30;
            for(j = 0;j < n;j ++)
            {
                if(!vis[j] && min > dist[j])
                {
                    min = dist[j];
                    k = j;
                }
            }
            vis[k] = 1;
            if(min != 1 << 30)
            {
                cnt++;
                sum += min;
            }
            for(j = 0;j < n;j ++)
            {
                if(!vis[j] && dist[j] > map[k][j])
                    dist[j] = map[k][j];
            }
        }
        if(cnt == n-1)
            printf("%d\n\n",sum);
        else
            printf("impossible\n\n");
    }
    return 0;
}