题目链接：https://www.luogu.com.cn/problem/U81904

错误点：#8

#include<bits/stdc++.h>
using namespace std;
const int N=5e5+5;
vector<pair<int,int> >g[N];
int n,k,maxn;
void dfs(int x,int fa,int dis)
{
	if(dis>maxn)
	{
		maxn=dis;
		k=x;
	}
	for(int i=0;i<g[x].size();++i)
	{
		int y=g[x][i].first,z=g[x][i].second;
		if(y==fa)
			continue;
		dfs(y,x,dis+z);
	}
	return;
}
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n-1;++i)
	{
		int x,y,z;
		scanf("%d%d%d",&x,&y,&z);
		g[x].push_back(make_pair(y,z));
		g[y].push_back(make_pair(x,z));	
	}
	maxn=-2e9;
	dfs(1,0,0);//返回k点，最大距离为maxn 
	maxn=-2e9;
	dfs(k,0,0);
	printf("%d",maxn);
	return 0;
}