C++

$\color{gold}{— > 蓝桥杯辅导课题解}$

思路：

树形dp

$code$

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

const int N = 1e5 + 10, M = N * 2;
typedef long long ll;

int n;
int w[N];
int h[N], e[M], ne[M], idx;
ll f[N]; // 状态数组

void add(int a, int b) { // 邻接表加边函数
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}

void dfs(int u, int father) { // father:是从那个点下来的
    f[u] = w[u];
    for (int i = h[u]; i != -1; i = ne[i]) {
        int j = e[i];
        if (j != father) { // 避免往回搜
            dfs(j, u);
            f[u] += max(0ll, f[j]);
        }
    }
}

int main() {
    cin >> n;
    memset(h, -1, sizeof h);
    for (int i = 1; i <= n; i ++) cin >> w[i];

    for (int i = 0; i < n - 1; i ++) {
        int a, b;
        cin >> a >> b;
        add(a, b), add(b, a);
    }

    dfs(1, -1);

    ll res = f[1];
    for (int i = 2; i <= n; i ++) res = max(res, f[i]); // 求一下最大连通块

    cout << res;

    return 0;
}