题目

一道比较好想的树形\(DP\)

完全可以用树形DP的基本思路，递归，然后取最优的方法。

\(Code\)

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
using namespace std;
int n, a, b, cnt, maxn, data[100100], dp[100100], lin[100010];
struct cym {
    int to, nex;
}e[100100];
inline void add(int f, int t)
{
    e[++cnt].to = t;
    e[cnt].nex = lin[f];
    lin[f] = cnt;
}
inline void dfs(int now, int fa)
{   
    dp[now] = data[now];
    for (int i = lin[now]; i; i = e[i].nex)
    {
        int to = e[i].to;
        if (to == fa) continue;
        dfs(to, now);
        dp[now] += max(0, dp[to]);
    }
    maxn = max(maxn, dp[now]);
}
int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%d", &data[i]), dp[i] = data[i];
    for (int i = 1; i < n; i++) 
    {
        scanf("%d%d", &a, &b);
        add(a, b), add(b, a);
    }
    dfs(1, 0);
/*  for (int i = 1; i <= n; i++)
        if (!dp[i])
            dfs(i, 0);
*/
    printf("%d", maxn); 
}