求最大的子树之和

维护包含当前节点的最大子树之和就好了

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1e6+10;
ll w[N];
vector<int>g[N];
ll f[N];
ll res;ll dfs(int u,int father){f[u] = w[u];for(auto &t:g[u]){if(t==father)continue;ll tem = dfs(t,u);f[u]+=max(0ll,tem);}res = max(res,f[u]);//cout<<u<<" "<<f[u]<<"\n";return f[u];}int main()
{int n;cin>>n;for(int i=1;i<=n;i++)cin>>w[i];for(int i=1;i<n;i++){int a,b;cin>>a>>b;g[a].push_back(b);g[b].push_back(a);}dfs(1,-1);cout<<res;}