poj 1655 Balancing Act

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树dp 树的重心

简单题,找树的重心，有多个重心，输出标号较小的，另外输出重心下最大分支的节点数

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#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
#define N 20010
#define INF 0x3f3f3f3f
#define cl(xx,yy) memset((xx),(yy),sizeof((xx)))
#define pb push_back

vector<int>e[N];
int n,cnt[N],Max[N],root,ans;

void dfs(int u,int fa){
	cnt[u] = 1;
	for(int i = 0; i < e[u].size(); i++){
		int v = e[u][i];
		if(v == fa) continue;
		dfs(v,u);
		cnt[u] += cnt[v];
		Max[u] = max(Max[u],cnt[v]);
	}
}

void find(int u,int fa){
	int tmp = cnt[1] - cnt[u];
	tmp = max(tmp,Max[u]);
	if(tmp < ans){
		ans = tmp; root = u;
	}
	else if(tmp == ans && u < root){
		ans = tmp; root = u;
	}
	for(int i = 0; i < e[u].size(); i++){
		int v = e[u][i];
		if(v == fa) continue;
		find(v,u);
	}
}

int main(){
	int T;
	scanf("%d",&T);
	while(T--){
		scanf("%d",&n);
		for(int i = 1; i <= n; i++)
			e[i].clear();
		for(int i = 1; i < n; i++){
			int u,v;
			scanf("%d%d",&u,&v);
			e[u].pb(v); e[v].pb(u);
		}
		cl(Max,0); root = -1; ans = INF;
		dfs(1,-1);
		find(1,-1);
		printf("%d %d\n",root,ans);
	}
	return 0;
}