树形DP

#include<bits/stdc++.h>
using namespace std;

const int maxn = 6010;
int N, R[maxn], h, p[maxn] = {0}, dp[maxn][2] = {0};
vector<int> g[maxn];

void dfs(int x) {
    dp[x][1] = R[x];
    for(auto c : g[x]) {
        dfs(c);
        dp[x][0] += max(dp[c][0], dp[c][1]);
        dp[x][1] += dp[c][0];
    }
}

int main() {
    cin >> N;
    for(int i = 1; i <= N; i++) scanf("%d", R + i);
    int a, b;
    for(int i = 0; i < N - 1; i++) scanf("%d%d", &a, &b), g[b].push_back(a), p[a] = 1;
    for(int i = 1; i <= N; i++) if(!p[i]) h = i;
    dfs(h);
    cout << max(dp[h][0], dp[h][1]);
}