51nod 1424 零树

书上跑个DP。

#include<bits/stdc++.h>using namespace std;const int MAXN=100100;long long v[MAXN],add[MAXN],sub[MAXN];vector<int> vec[MAXN];void dfs(int x,int fa){for(int i=0;i<vec[x].size();i++){if(vec[x][i]==fa)continue;dfs(vec[x][i],x);add[x]=max(add[x],add[vec[x][i]]);sub[x]=max(sub[x],sub[vec[x][i]]);}v[x]+=add[x]-sub[x];if(v[x]>0)sub[x]+=v[x];elseadd[x]+=-v[x];}int main(){long long n,a,b,i;while(~scanf("%lld",&n)){for(i=1;i<=n;i++)vec[i].clear();for(i=1;i<n;i++){scanf("%lld%lld",&a,&b);vec[a].push_back(b);vec[b].push_back(a);}for(i=1;i<=n;i++)scanf("%lld",&v[i]);memset(add,0,sizeof(add));memset(sub,0,sizeof(sub));dfs(1,-1);printf("%lld\n",add[1]+sub[1]);}}