用的换根DP，但是TLE，应该是dfs有问题

#include <bits/stdc++.h>
#define maxx(a,b) a>b?a:b
#define nulls ios::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
#define ll long long
using namespace std;
const int N = 1e6+10;
ll head[N*2] , tot = 0;
ll n , m , cnt;
ll g[N] , f[N] , siz[N];
struct node{
	ll next , w , to;
}edge[2*N];
void init() {
	memset(head , -1 , sizeof head);
	tot = 0;
}
void add(ll x ,ll y ) {
	edge[tot].to = y;
	edge[tot].next = head[x];
	head[x] = tot++; 
}
void add_ (ll x , ll y) {
	add(x , y);
	add(y , x);
}
void add(ll x ,ll y , ll z) {
	edge[tot].to = y;
	edge[tot].next = head[x];
	edge[tot].w = z;
	head[x] = tot++; 
}
void add_ (ll x , ll y , ll z) {
	add(x , y , z);
	add(y , x , z);
}
void dfs(ll u , ll fa) {
	siz[u] = 1;
	g[u] = 0;
	for(int i = head[u] ; ~i ; i = edge[i].next) {
		int v = edge[i].to;
		if(v == fa) continue;
		dfs(v , u);
		siz[u] += siz[v];
		g[u] += g[v] + siz[v];
	}
} 
void sdf(ll u , ll fa) {
	for(int i = head[u] ; ~i ; i = edge[i].next) {
		int v = edge[i].to;
		if(v == fa) continue;
		f[v] = f[u] + siz[1] - 2*siz[v];
		sdf(v ,u);
	}
}
int main() {
	nulls
	cin >> n;
	for(int i = 1 ; i < n ; i++) {
		ll x , y;
		cin >> x >> y;
		add_(x , y);
	}
	dfs(1 , 0);
	f[1] = g[1];
	sdf(1 , 0);
	ll ans = 0 , x = 0;
	for(int i = 1 ; i <= n ; i++) {
		if(f[i] > ans) {
			ans = f[i];
			x = i;
		}
	}
	cout << x;
}