![](https://img2020.cnblogs.com/blog/2167276/202107/2167276-20210717112037186-1000596061.png)
AcWing 1207.大臣的旅费
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 1e5+10,M=2e5+20;
ll dist[N];
int h[M],ne[M],e[M],w[M],idx;
void add(int a,int b,int c)
{
e[idx]=b,ne[idx]=h[a],w[idx]=c,h[a]=idx++;
}
void dfs(int st,int father,ll distance)
{
dist[st] = distance;
for(int i = h[st];~i;i=ne[i])
if(e[i]!=father) dfs(e[i],st,dist[st]+w[i]);
}
ll cal(ll k)
{
return k*10+(k+1ll)*k/2;
}
int main()
{
memset(h,-1,sizeof(h));
int A,B,C;
int n;
cin>>n;
for(int i=0;i<n-1;i++)
{
cin>>A>>B>>C;
add(A,B,C);add(B,A,C);
}
memset(dist,0,sizeof(dist));
dfs(1,-1,0);
int u=1;
for(int i=2;i<=n;i++)
if(dist[i]>dist[u])u=i;
dfs(u,-1,0);
ll kio=dist[1];
for(int i=2;i<=n;i++)
if(dist[i]>kio)kio=dist[i];
cout<<kio*10+kio*(kio+1)/2;
return 0;
}