rt，一道数的直径题。跑到dfs时直接趋势

#include<bits/stdc++.h>
using namespace std;

int n,m;
vector<int>g[10001];
vector<int>go,vis;int node;

void dfs(int u){
	for (int i=0;i<g[u].size();++i){
		int t=g[u][i];
		if (vis[t]==0){
			vis[t]=1;
			go[t]=go[u]+1;
			if (go[node]<go[t])node=t;
			dfs(t);
			vis[t]=0;
		}
	}
	return ;
}

int main(){
	cin>>n;
	m=n-1;
	for (int i=0;i<m;++i){
		int x,y;
		cin>>x>>y;
		g[x].push_back(y);
		g[y].push_back(x);
	}
	vis[1]=1;
	dfs(1);
  	go[node]=0;
	vis[node]=1;
	dfs(node);
  	cout<<go[node];
	return 0;
}