目标：Java web开发

问题树的重心

import java.io.*;
public class Main {
    static final int N=(int)1e5+10,M=N<<1,INF=(int)1e9;
    static int n,idx,min=INF;
    static int[] h=new int[N],e=new int[M],ne=new int[M];
    static boolean[] status=new boolean[N];
    static BufferedReader bf=new BufferedReader(new InputStreamReader(System.in)));
    static void add(int u,int v) {
        e[idx]=v;
        ne[idx]=h[u];
        h[u]=idx++;
    }
    static int dfs(int u){
        status[u]=true;
        int s,sum=1,max=-INF;
        for (int i=h[u];i!=-1;i=ne[i]){
            if(status[e[i]]) continue;
            s=dfs(e[i]);
            max=Math.max(max,s);
            sum+=s;
        }
        max=Math.max(max,n-sum);
        min=Math.min(min,max);
        return sum;
    }
    public static void main(String[] args)throws IOException{
        bf.nextToken();
        n = (int)st.nval;
        for (int i = 1; i <= n; ++i) {
            h[i] = -1;
        }
        int a, b;
        for (int i = 1; i < n; ++i) {
            st.nextToken();
            a=(int)st.nval;
            st.nextToken();
            b=(int)st.nval;
            add(a, b);
            add(b, a);
        }
        dfs(1);
        bw.write(min + "");
        bw.close();
    }
}