Jungle Roads HDU - 1301 prim

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
const int N=30;
int map[N][N];
bool vis[N];
void Prim(int n)
{
    int len=0,count=0;
    vis[0] = 1;
    while(count<n-1)
    {
        int tmp=-1,u;
        for(int i=0;i<n;++i){
            if(!vis[i]) 
                continue;
            for(int j=0;j<n;++j)
                if(map[i][j]!=-1&&!vis[j]&&(map[i][j]<tmp||tmp==-1))
                    tmp=map[i][j],u=j;
        }
        if(tmp!=-1)
        {
            ++count;
            vis[u]=1;
            len+=tmp;
        }
    }
    cout<<len<<endl;
}
int main()
{
    int n;
    char node[2];
    while(cin>>n&&n)
    {
        memset(map,-1,sizeof(map));
        memset(vis,0,sizeof(vis));
        int m=n-1;
        while(m--)
        {
            int count;
            cin>>node>>count;
            int a=node[0]-'A';
            while(count--)
            {
                int len;
                cin>>node>>len;
                int b=node[0]-'A';
                map[a][b]=map[b][a]=len;
            }
        }
        Prim(n);
    }
    return 0;
}