树形dp

#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
const int N = 1e5 + 5, M = N * 2;
typedef long long LL;
int n, h[N], e[M], ne[M], idx;
LL ans, g[N];
void add(int a, int b){
    e[idx] = b; ne[idx] = h[a]; h[a] = idx ++;
}

LL dfs(int u, int fa){
    LL sum = g[u];
    for(int i = h[u]; i != -1; i = ne[i]){
        int j = e[i];
        if(j != fa){
        LL d = dfs(j, u);
        if(d > 0) sum += d;
        }
    }
    ans = max(ans, sum);
    return sum;
}


int main(){
    ans = -2e9;
    memset(h, -1, sizeof h);
    cin >> n;
    for(int i = 1; i <= n; i ++ ){
        scanf("%lld", &g[i]);
    }
    for(int i = 1; i < n; i ++ ) {
        int a, b;
        scanf("%d%d", &a, &b);
        add(a, b); add(b, a);
    }
    dfs(1, -1); // u, fa
    cout << ans << endl;
    return 0;
}