1207. 大臣的旅费

https://www.acwing.com/problem/content/1209/

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
const int N = 1e5+10;
int n;
struct Edge
{
    int id,w;
};
vector<Edge> h[N];
int dist[N];

void dfs(int u,int f,int distance)
{
    dist[u]=distance;
    for(auto node:h[u])
        if(node.id != f)
            dfs(node.id,u,distance+node.w);
}

int main()
{
    cin >> n;
    for(int i=0;i<n-1;i++)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        h[a].push_back({b,c});
        h[b].push_back({a,c});
    }
    dfs(1,-1,0);
    int u=1;
    for(int i=1;i<=n;i++)
    {
        if(dist[i]>dist[u])u=i;
    }
    dfs(u,-1,0);
    for(int i=1;i<=n;i++)
    {
        if(dist[i]>dist[u])u=i;
    }
    int s=dist[u];
    printf("%lld",s*10+s*(s+1ll)/2);
    return 0;
}