思路为树的重心，一遍dfs找重心，二遍dfs找答案，但后面神奇报零，求大佬解答。（样例能过）

#include <iostream>
#include <vector>
#include <cstring>
#define int long long 

using namespace std;

const int N = 1e5 + 5;

struct qq{
	
	int u,v,w;
	
}d[N];

int n,c[N],f[N],siz[N],ans,maxsiz[N],s,dis[N],sum;
bool f1;
vector <pair<int,int> > g[N];

void add (int u,int v,int w){
	
	g[u].push_back({v,w});
	g[v].push_back({u,w});
}

void dfs (int x,int father){
	
//	f[x] = c[x];
	siz[x] = c[x];
	f1 = 0;
	for (auto y:g[x]){
		
		int v = y.first;
//		int w = y.second;
		
		if (v == father) continue;
		
		dfs (v,x);
		siz[x] += siz[v];
//		ans[x] = siz[v] * f[v];
		if (siz[v] * 2 > sum) f1 = 1;
	}
	if (siz[x] * 2 < sum) f1 = 1;
//	maxsiz[x] = max (maxsiz[x],siz[v]);
	if (!f1){
		
		s = x;
		
	}
}

void dfs1 (int x,int father){
	
	siz[x] = c[x];
	
	for (auto y:g[x]){
		
		int v = y.first;
		int w = y.second;
		if (v == father) continue;
		dfs1 (v,x);
		siz[x] += siz[v];
		ans += 1ll * siz[v] * w;
	}
	
}

signed main(){
	
	cin >> n;
	
	for (int i = 1;i <= n;i ++){
		
		cin >> c[i];
		
		sum += c[i];
		
	}
	
	for (int i = 1;i <= n - 1;i ++){
		
		cin >> d[i].u >> d[i].v >> d[i].w;
		
		add (d[i].u,d[i].v,d[i].w);
		
	}
	
	dfs (1,0);
	
//	for (int i = 1;i <= n;i ++){
//		
//		if (maxsiz[i] < maxsiz[id]){
//			
//			id = i;
//			
//		}
//		
//	}
	
//	dis[id] = 0;
	memset(siz,0,sizeof(siz));
	
	dfs1(s,0);
//	for (int i = 1;i <= n;i ++){
//		
//		cout << ans[i] << '\n';
//		
//	}
	cout << ans << '\n';
	return 0;
}