villages problem a

Problem Description
There are N villages, which are numbered from 1 to N, and you should build some roads such that every two villages can connect to each other. We say two village A and B are connected, if and only if there is a road between A and B, or there exists a village C such that there is a road between A and C, and C and B are connected. We know that there are already some  roads between some villages and your job is the build some roads such that all  the villages are connect and the length of all the roads built is  minimum.
 

#include<iostream>#include<cstdio>#include<cstring>using namespace std;const int N=110;const int INF=0x3f3f3f3f;int n,ans;int map[N][N],dis[N],vis[N];void Prim(){    int i;    for(i=1;i<=n;i++){        dis[i]=map[1][i];        vis[i]=0;    }    dis[1]=0;    vis[1]=1;    int j,k,tmp;    for(i=1;i<=n;i++){        tmp=INF;        for(j=1;j<=n;j++)            if(!vis[j] && tmp>dis[j]){                k=j;                tmp=dis[j];            }        if(tmp==INF)            break;        vis[k]=1;        ans+=dis[k];        for(j=1;j<=n;j++)            if(!vis[j] && dis[j]>map[k][j])                dis[j]=map[k][j];    }}int main(){    //freopen("input.txt","r",stdin);    while(~scanf("%d",&n)){        for(int i=1;i<=n;i++)            for(int j=1;j<=n;j++)                scanf("%d",&map[i][j]);        int q,a,b;        scanf("%d",&q);        while(q--){            scanf("%d%d",&a,&b);            map[a][b]=map[b][a]=0;        }        ans=0;        Prim();        printf("%d\n",ans);    }    return 0;}