典型树上dp，直接暴力算会超时，小心呀
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<vector>
#define maxn 100010
using namespace std;
typedef long long ll;
struct Node {
int p;
ll len;
Node(int a, ll b) :p(a), len(b) {}
};
vector<Node>G[maxn];
void insert(int be, int en,ll len) {
G[be].push_back(Node(en, len));
}
int n, m;
ll sum = 0;
ll ran[maxn];
ll ans[maxn];
ll list[maxn];
int dfs1(int x, int fa) {
ll k = 0;
for (int i = 0; i < G[x].size(); i++) {
int p = G[x][i].p;
ll ln = G[x][i].len;
if (p == fa) continue;
dfs1(p, x);
k = ran[p];
ans[x] += (ans[p] + ran[p] * ln);
ran[x] += ran[p];
}
return 0;
}
int dfs(int x, int fa) {
for (int i = 0; i < G[x].size(); i++) {
int p = G[x][i].p;
ll ln = G[x][i].len;
if (p == fa) continue;
ans[p] += ans[x] - (ans[p] + ran[p] * ln) + (sum - ran[p])*ln;
dfs(p, x);
}
return 0;
}
int main() {
scanf("%d", &n);
m = n - 1;
for (int i = 1; i <= n; i++) {
scanf("%lld", &list[i]);
sum += list[i];
ran[i] = list[i];
}
int be, en;
ll len;
for (int i = 0; i < m; i++) {
scanf("%d%d%lld", &be, &en, &len);
insert(be, en, len);
insert(en, be, len);
}
dfs1(1, -1);
dfs(1, -1);
ll cns = 10000000000000000;
for (int i = 1; i <= n; i++) {
cns = min(cns, ans[i]);
}
printf("%lld
", cns);
return 0;
}