Codeforces Round #168 (Div. 1) B. Zero Tree 树形dp

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 #define MS(a) memset(a,0,sizeof(a))
 5 #define MP make_pair
 6 #define PB push_back
 7 const int INF = 0x3f3f3f3f;
 8 const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
 9 inline ll read(){
10     ll x=0,f=1;char ch=getchar();
11     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
12     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
13     return x*f;
14 }
15 //////////////////////////////////////////////////////////////////////////
16 const int maxn = 1e5+10;
17 
18 vector<int> g[maxn];
19 int n;
20 ll a[maxn],up[maxn],down[maxn];
21 
22 void dfs(int u,int fa){
23     for(int i=0; i<(int)g[u].size(); i++){
24         int v = g[u][i];
25         if(v == fa) continue;
26         dfs(v,u);
27         up[u] = max(up[u],up[v]);
28         down[u] = max(down[u],down[v]);
29     }
30     a[u] = a[u]+up[u]-down[u];
31     if(a[u] > 0) down[u] += a[u];
32     else up[u] -= a[u];
33 }
34 
35 int main(){
36     cin >> n;
37     for(int i=1; i<n; i++){
38         int u,v; cin>>u>>v;
39         g[u].push_back(v);
40         g[v].push_back(u);
41     }
42     for(int i=1; i<=n; i++)
43         cin >> a[i];
44     dfs(1,-1);
45 
46     cout << up[1]+down[1] << endl;
47 
48     return 0;
49 }