Codeforces 274B Zero Tree

 1 // File Name: 274b.cpp
 2 // Author: darkdream
 3 // Created Time: 2015年03月12日 星期四 21时26分55秒
 4 
 5 #include<vector>
 6 #include<list>
 7 #include<map>
 8 #include<set>
 9 #include<deque>
10 #include<stack>
11 #include<bitset>
12 #include<algorithm>
13 #include<functional>
14 #include<numeric>
15 #include<utility>
16 #include<sstream>
17 #include<iostream>
18 #include<iomanip>
19 #include<cstdio>
20 #include<cmath>
21 #include<cstdlib>
22 #include<cstring>
23 #include<ctime>
24 #define LL long long
25 #define maxn 100105
26 using namespace std;
27 vector<int> mp[maxn];
28 LL v[maxn];
29 LL dp[maxn][2];
30 LL ans = 0 ;
31 void dfs(int k , int la)
32 {
33   
34    LL maxi = 0 ; 
35    LL maxd = 0 ; 
36   for(int i = 0 ;i < mp[k].size();i ++)
37    {
38        if(mp[k][i] == la)
39            continue;
40        dfs(mp[k][i],k);
41        maxi = max(maxi,dp[mp[k][i]][1]);
42        maxd = max(maxd,dp[mp[k][i]][0]);
43    }
44    v[k] += maxi;
45    v[k] -= maxd;
46    dp[k][0] = maxd;
47    dp[k][1] = maxi;
48    if(v[k] > 0)
49        dp[k][0] += v[k];
50    else dp[k][1] += (-v[k]);
51 }
52 int main(){
53    int n;
54    scanf("%d",&n);
55    for(int i = 1;i <n;i ++)
56    {
57       int ta , tb; 
58       scanf("%d %d",&ta,&tb);
59       mp[ta].push_back(tb);
60       mp[tb].push_back(ta);
61    }
62    for(int i = 1;i <= n;i ++)
63    {
64       cin >> v[i];
65    }
66    dfs(1,0);
67   // for(int i = 1;i <= n;i ++)
68   // {
69   //    cout << dp[i][0] << " " << dp[i][1] << endl; 
70   // }
71    cout << dp[1][0] + dp[1][1] ;
72 return 0;
73 }