1207. 大臣的旅费

思路：
由题意求最多的花费的路费，相当于是求树的直径，树的直径则为最大值
，另外由于是稀疏图，所以用邻接表来存储

代码：

# include<iostream>
# include<cstdio>
# include<cstring>
# include<algorithm>
# include<vector>
using namespace std;

const int N = 100010;
struct Edge
{
    
    
    int id,w;  
};
int n;
vector<Edge> h[N];
int dis[N];

void dfs(int u,int father,int distance)
{
    
    
    dis[u] = distance;
    for(auto node : h[u])//遍历该节点的所有儿子
    {
    
    
        if(node.id != father)//防止往回走
        {
    
    
            dfs(node.id,u,distance + node.w);
        }
    }
}

int main()
{
    
    
    scanf("%d",&n);
    for(int i = 0;i < n;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(dis[i] > dis[u])
        {
    
    
            u = i;
        }
    }
    
    dfs(u,-1,0);
    
    for(int i = 1;i <= n;i++)
    {
    
    
        if(dis[i] > dis[u])
        {
    
    
            u = i;
        }
    }
    int s = dis[u];
    printf("%lld\n",10 * s + s * (s + 1ll) / 2);
    
    return 0;
}