洛谷P2607 [ZJOI2008]骑士 基环树动归
Code:
#include<algorithm>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
typedef long long ll;
const int maxn=1000000+233;
const int N=1000000+233;
int A[N],B[N];
ll G[N],F[N];
int head[maxn*2],nex[maxn*2],to[maxn*2],val[maxn],vis[maxn];
int cnt,num,root;
struct Circle{
int p[maxn];
void init(){
for(int i=1;i<maxn-12;++i)p[i]=i;
}
int find(int x){
if(p[x]==x)return x;
else return p[x]=find(p[x]);
}
int query(int x,int y){
int a=find(x);int b=find(y);
if(a!=b)p[a]=b;
if(a==b)return 1;
return 0;
}
}S;
void add_edge(int u,int v){
nex[++cnt]=head[u],to[cnt]=v,head[u]=cnt;
}
void dfs(int u,int fa,int c){
G[u]=val[u],F[u]=0,vis[u]=1;
for(int v=head[u];v;v=nex[v])
if(to[v]!=fa){
dfs(to[v],u,c);
G[u]+=F[to[v]];
F[u]+=max(F[to[v]],G[to[v]]);
}
}
int main(){
ll ans=0;
S.init();
int n;
scanf("%d",&n);
for(int i=1;i<=n;++i){
int a,b;scanf("%d%d",&a,&b);
val[i]=a;
int flag=S.query(i,b);
if(flag==0){
add_edge(i,b);
add_edge(b,i);
}
if(flag==1)A[++num]=b,B[num]=i;
}
for(int i=1;i<=num;++i){
int a=A[i],b=B[i];
ll sum1,sum2;
root=b;dfs(b,-1,a);sum1=F[b];
root=a;dfs(a,-1,b);sum2=F[a];
ans+=max(sum1,sum2);
}
for(int i=1;i<=n;++i)
if(!vis[i]){
dfs(i,-1,-2);
ans+=max(F[i],G[i]);
}
printf("%lld",ans);
return 0;
}