bzoj 1040

对每棵树做DP，有环特判即可。。

DP方程居然写错了。。。

#include<bits/stdc++.h>
#define inc(i,l,r) for(i=l;i<=r;i++)
#define dec(i,l,r) for(i=l;i>=r;i--)
#define mem(a) memset(a,0,sizeof(a))
#define inf 1e9
#define ll long long
#define succ(x) (1<<x)
#define NM 1000000+5
using namespace std;
int read(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
    while(isdigit(ch))x=x*10+ch-'0',ch=getchar();
    return x*f;
}
struct edge{
    int t,v;
    edge *next;
}e[2*NM],*h[NM];
int a[NM],f[NM],i,n,s,X,Y,t;
ll ans,d[NM],g[NM],_x,_y;
bool v[NM],V[NM];
void add(int x,int y){
    e[++s].t=y;e[s].next=h[x];h[x]=e+s;
}
void dfs(int x,int k){
    v[x]++;V[x]=true;
    for(edge *j=h[x];j;j=j->next)
    if(j->t!=k){
        if(X==0&&v[j->t]){
            X=x;Y=j->t;
        }
        if(!v[j->t]){
        dfs(j->t,x);
        g[x]+=max(d[j->t],g[j->t]);
        d[x]+=g[j->t];
        }
    }
    if(x!=X)d[x]+=a[x];
}
int main(){
    n=read();
    inc(i,1,n)f[i]=i;
    inc(i,1,n){
        a[i]=read();t=read();
        add(i,t);add(t,i);
    }
    inc(i,1,n)
    if(!V[i]){
        X=0;
        mem(d);mem(g);mem(v);
        dfs(i,0);
        _x=d[i];_y=g[i];
        mem(d);mem(g);mem(v);
        X=Y;
        dfs(i,0);
        _x=max(_x,d[i]);_y=max(_y,g[i]);
        ans+=max(_x,_y);
    }
    printf("%lld
",ans);
    return 0;
}