10162. 「一本通 5.2 练习 5」骑士

#include<algorithm>
#include<bitset>
#include<complex>
#include<deque>
#include<exception>
#include<fstream>
#include<functional>
#include<iomanip>
#include<ios>
#include<iosfwd>
#include<iostream>
#include<istream>
#include<iterator>
#include<limits>
#include<list>
#include<locale>
#include<map>
#include<memory>
#include<new>
#include<numeric>
#include<ostream>
#include<queue>
#include<set>
#include<sstream>
#include<stack>
#include<stdexcept>
#include<streambuf>
#include<string>
#include<typeinfo>
#include<utility>
#include<valarray>
#include<vector>
#include<cctype>
#include<cerrno>
#include<cfloat>
#include<ciso646>
#include<climits>
#include<clocale>
#include<cmath>
#include<csetjmp>
#include<csignal>
#include<cstdarg>
#include<cstddef>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#define int long long
using namespace std;
inline int read(){
    int res=0,f=1;char ch=getchar();
    while(ch<'0'ch>'9'){if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9') res=res*10+ch-'0',ch=getchar();
    return res*f;
}
inline void write(int x){
    if(x<0) putchar('-'),x=-x;
    if(x<10) putchar(x+'0');
    else{
        write(x/10);
        putchar(x%10+'0');
    }
}
int n,v[1000010],a[1000010],f[1000010][2],in[1000010],rt=1,vis[1000010],d[1000010],t;
int fir[1000010],nxt[1000010],w[1000010],son[1000010],tot,fa[1000010],ans;
void add(int x,int y){
    ++tot;
    son[tot]=y;
    nxt[tot]=fir[x];
    fir[x]=tot;
}
void TreeDp(int x){
    vis[x]=1;
    f[x][0]=0;f[x][1]=a[x];
    for(int i=fir[x];i;i=nxt[i]){
        int to=son[i];
        if(to==rt){
            f[to][1]=-2e9;continue ;
        }
        TreeDp(to);
        f[x][0]+=max(f[to][0],f[to][1]);
        f[x][1]+=f[to][0];
    }
}
void circle(int x){
    rt=x;
    while(vis[rt]==0){
        vis[rt]=1;
        rt=fa[rt];
    }
    TreeDp(rt);
    long long tmp=max(f[rt][0],f[rt][1]);
    rt=fa[rt];
    TreeDp(rt);
    long long temp=max(f[rt][0],f[rt][1]);
    ans+=max(tmp,temp);
}
signed main(){
    n=read();
    for(int i=1;i<=n;i++){
        a[i]=read();
        int x=read();
        add(x,i);
        fa[i]=x;
    }
    for(int i=1;i<=n;i++){
        if(vis[i]==0){
            circle(i);
        }
    }
    write(ans);putchar('\n');
    return 0;
}