POJ 1655 tree_dp?dfs?

/* ******************************************************************
dfs统计子节点个数更新root结点
****************************************************************** */
#include < iostream >
#include < vector >
using   namespace  std;
vector < int > tree[ 20001 ];
bool  visit[ 20001 ];
int  d[ 20001 ];
int  f[ 20001 ];
int  n;
void  dfs( int  root)
{
     int  i;
     for (i = 0 ;i < tree[root].size();i ++ )
    {
         if ( ! visit[tree[root][i]])
        {
            visit[tree[root][i]] = 1 ;
            dfs(tree[root][i]);
        }
    }
     for (i = 0 ;i < tree[root].size();i ++ )
        d[root] += d[tree[root][i]];
    d[root] += 1 ;
     int  sum = 0 ;
    f[root] = 0 ;
     for (i = 0 ;i < tree[root].size();i ++ )
    {
        f[root] = max(f[root],d[tree[root][i]]);
        sum += d[tree[root][i]];
    }
    f[root] = max(f[root],n - sum - 1 );
     return  ;
}
int  main()
{
     int  i,j,cas,c;
    scanf( " %d " , & cas);
     for (c = 1 ;c <= cas;c ++ )
    {
        scanf( " %d " , & n);
        memset(visit, 0 , sizeof (visit));
        memset(d, 0 , sizeof (d));
        memset(f, 0 , sizeof (f));
         for (i = 1 ;i <= n;i ++ )
        {
            tree[i].clear();
        }
         for (i = 1 ;i < n;i ++ )
        {
             int  a,b;
            scanf( " %d %d " , & a, & b);
            tree[b].push_back(a);
            tree[a].push_back(b);
        }
        visit[ 1 ] = 1 ;
        dfs( 1 );
         int  now = 0 ,best = INT_MAX;
         for (i = 1 ;i <= n;i ++ )
        {
             if (best > f[i])
            {
                best = f[i];
                now = i;
            }
        }
        printf( " %d %d\n " ,now,best);
    }
     return   0 ;
}