POJ 1251 最小生成树prim算法

还是最小生成树prim算法，套用的浙大模板

#include <iostream>
#define MAXN 28
#define inf 10000
typedef int elem_t;
using namespace std;
elem_t prim(int n,elem_t mat[MAXN][MAXN],int* pre){
    elem_t min[MAXN],ret=0;
    int v[MAXN],i,j,k;
    for (i=0;i<n;i++)
        min[i]=inf,v[i]=0,pre[i]=-1;
    for (min[j=0]=0;j<n;j++){
        for (k=-1,i=0;i<n;i++)
            if (!v[i]&&(k==-1||min[i]<min[k]))
                k=i;
            for (v[k]=1,ret+=min[k],i=0;i<n;i++)
                if (!v[i]&&mat[k][i]<min[i])
                    min[i]=mat[pre[i]=k][i];
    }
    return ret;
}

int main(){
    int n,m,i,j,result,q;
    int pre[MAXN];
    int distance[MAXN][MAXN];
    char s,e;
    while(cin>>n,n!=0){
        for (i = 0;i < n;i++)
            for (j = 0;j < n;j++)
                {
                    distance[i][j] = inf;
                }
        for(i = 0;i < n-1;i++){
            cin>>s>>m;
            for(j = 0;j < m;j++){
                cin>>e>>q;
                distance[s -'A'][e -'A'] = distance[e -'A'][s -'A'] = q;
            }
        }
        result  = prim(n,distance,pre);
        cout << result<<endl;
    }
    return 0;
}