[poj1655]Balancing Act

树重心裸题。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int N=20005;
struct graph{
	int nxt,to;
}e[N<<1];
int g[N],w[N],siz[N],n,t,cnt;
void adde(int x,int y){
	e[++cnt].nxt=g[x];g[x]=cnt;e[cnt].to=y;
}
void dfs(int u){
	siz[u]=1;
	for(int i=g[u];i;i=e[i].nxt)
		if(!siz[e[i].to]){
			dfs(e[i].to);
			siz[u]+=siz[e[i].to];
			w[u]=max(siz[e[i].to],w[u]);
		}
	w[u]=max(w[u],n-siz[u]);
}
int main(){
	scanf("%d",&t);
	while(t--){
		scanf("%d",&n);
		memset(g,0,sizeof(g));cnt=0;
		memset(siz,0,sizeof(siz));
		memset(w,0,sizeof(w));
		for(int i=1,x,y;i<n;++i){
			scanf("%d%d",&x,&y);
			adde(x,y);adde(y,x);
		}
		dfs(1);
		int ans=n,id=0;
		for(int i=1;i<=n;++i)
			if(w[i]<ans){
				ans=w[i];id=i;
			} 
		printf("%d %d\n",id,ans);
	}
	return 0;
}