https://codeforces.com/problemset/problem/1092/F

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思路：奶牛聚会的原题

#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=2e5+1000;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL siz[maxn],dp[maxn],c[maxn];
vector<LL>g[maxn];
void dfs1(LL u,LL fa,LL dep){
     siz[u]=c[u];
     for(LL i=0;i<g[u].size();i++){
         LL v=g[u][i];
         if(v==fa) continue;
         dp[1]+=dep*c[v];
         dfs1(v,u,dep+1);
         siz[u]+=siz[v];
     }
}
void dfs2(LL u,LL fa){
    for(LL i=0;i<g[u].size();i++){
        LL v=g[u][i];
        if(v==fa) continue;
        dp[v]=(siz[1]-siz[v]*2)*1+dp[u];
        dfs2(v,u);
    }
}
int main(void){
   cin.tie(0);std::ios::sync_with_stdio(false);
   LL n;cin>>n;
   for(LL i=1;i<=n;i++) cin>>c[i];
   for(LL i=1;i<n;i++){
       LL u,v;cin>>u>>v;
       g[u].push_back(v);g[v].push_back(u);
   }
   dfs1(1,-1,1);
   dfs2(1,-1);
   LL ans=-1;
   for(LL i=1;i<=n;i++){
       ans=max(ans,dp[i]);
   }
   cout<<ans<<"\n";
   return 0;
}