General
 
 
# Author Problem Lang Verdict Time Memory Sent Judged  
108320903 Practice:
luogu_bot1
835F - 34 GNU C++11 Accepted 1170 ms 35968 KB 2021-02-23 19:09:21 2021-02-23 19:09:21
 
 
→ Source
#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=200005,INF=1e18+5;
struct edge{
	int to;
	int wei;
	int nxt;
}e[N*2];
int n,tot=0,cnt=0,ans1=0,ans2=INF,res,head[N],cir[N],vis[N],f[N],we[N],l[N],l0[N],r[N],r0[N];
void add(int x,int y,int w){
	e[++tot]=(edge){y,w,head[x]};
	head[x]=tot;
}
int get_cir(int x,int fa=-1){
	if(vis[x]){
		return x;
	} 
	else{
		vis[x]=-1;
	}
	for(int i=head[x];i;i=e[i].nxt){
		if(e[i].to!=fa){
			res=get_cir(e[i].to,x);
			if(res){
				return cir[++cnt]=x,we[cnt]=e[i].wei,vis[x]=1,res==x?0:res;
			} 
		}
	}
	return 0;
}
void dfs(int x,int fa=-1){
	for(int i=head[x];i;i=e[i].nxt)
		if(vis[e[i].to]!=1&&e[i].to!=fa)
			dfs(e[i].to,x),ans1=max(ans1,f[x]+f[e[i].to]+e[i].wei),f[x]=max(f[x],f[e[i].to]+e[i].wei);
}
signed main(){
	cin>>n;
	memset(vis,0,sizeof(vis));
	memset(f,0,sizeof(f));
	for(int i=1;i<=n;i++){
		int x,y,z;
		cin>>x>>y>>z;
		add(x,y,z);
		add(y,x,z);
	}
	get_cir(1);
	we[0]=0;
	for(int i=1;i<=cnt;i++){
		dfs(cir[i]);
		we[i]+=we[i-1];
	}
	res=l[0]=l0[0]=-INF;
	for(int i=1;i<=cnt;i++){
		l0[i]=max(l0[i-1],f[cir[i]]+we[i]+res);
		l[i]=max(l[i-1],f[cir[i]]+we[i]);
		res=max(res,f[cir[i]]-we[i]);
	}
	res=r[cnt+1]=r0[cnt+1]=-INF;
	for(int i=cnt;i>=1;i--){
		r0[i]=max(r0[i+1],f[cir[i]]-we[i]+res);
		r[i]=max(r[i+1],f[cir[i]]+we[cnt]-we[i]);
		res=max(res,f[cir[i]]+we[i]);
	}
	for(int i=1;i<=cnt;i++){
		ans2=min(ans2,max(l[i-1]+r[i],max(l0[i-1],r0[i])));
	}
	cout<<max(ans1,ans2)<<endl;
	return 0;
}
 
 
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