连样例都没过的代码（输出了20）：

#include <bits/stdc++.h>
using namespace std;
const int N = 15e2 + 10;
const int INF = 0x3f3f3f;

int n;
int a[N];
int dp[N][3];  // u 被父亲看住(0)、被自己看住(1)、被儿子看住(2)
vector <int> g[N];
int fa[N];

void dfs(int u)
{
	dp[u][0] = 0;
	dp[u][1] = a[u];
	dp[u][2] = 0;
	int d = INF;
	for (int i=0; i<g[u].size(); i++)
	{
		int v = g[u][i];
		dfs(v);
		dp[u][0] += min(dp[v][1], dp[v][2]);
		dp[u][1] += min(dp[v][0], min(dp[v][1], dp[v][2]));
		dp[u][2] += min(dp[v][1], dp[v][2]);
		if (dp[v][1] < dp[v][2]) d = 0;
		else d = min(d, dp[v][1] - dp[v][2]);
	}
	dp[u][2] += d;
}

int main()
{
	cin >> n;
	for (int i=1; i<=n; i++)
	{
		int u, v, m;
		cin >> u >> a[u] >> m;
		for (int j=1; j<=m; j++)
		{
			cin >> v;
			g[u].push_back(v);
			fa[v] = u;
		}
	}
	int root = 0;
	for (int i=1; i; i=fa[i])
	{
		if (fa[i] == 0)
		{
			root = i;
			break;
		}
	}
	dfs(root);
	cout << min(dp[root][1], dp[root][2]) << endl;
	return 0;
}

但AC了