Build The Electric System

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=2966

prim:

#include<stdio.h>
#include<string.h>
const int INF = 1<<28 ;
#define maxn 510
int map[maxn][maxn], dis[maxn], visited[maxn] ;
int main()
{
    int t, a, b, k, n, e, minco, min ;
    int i, j ;
    int tt ;
    scanf("%d", &t) ;
    while(t--)
    {
        memset(visited, 0, sizeof(visited)) ;
        minco = 0 ;
        scanf("%d%d", &n, &e) ;
        for(i=0; i<n; i++)
        {
            for(j=0; j<n; j++)
            {
                map[i][j] = INF ;
            }
        }
        for(i=0; i<e; i++)
        {
            scanf("%d%d%d",&a, &b, &k) ;
            map[a][b] = map[b][a] = k ;
        }
        for(j=0; j<n; j++)
        dis[j] = map[0][j] ;
        visited[0] = 1 ;
        for(i=0; i<n; i++)
        {
           min = INF ;
           for(j=0; j<n; j++)
           {
               if(!visited[j]&&min>dis[j])
               {
                   min = dis[j] ;
                   tt = j ;
               }
           }
           if(min!=INF)
           minco += min ;
           visited[tt] = 1 ;
           for(j=0; j<n; j++)
           {
               if(!visited[j]&&dis[j]>map[tt][j])
               {
                   dis[j] = map[tt][j] ;
               }
           }
        }
        printf("%d\n", minco) ;
    }
    return 0 ;
}