求条树的直径

#include<bits/stdc++.h>
#define PII pair<int,int>
#define fi first
#define se second
using namespace std;
int n;
vector<PII>g[500005];
int dist1[500005];
int dist2[500005];
int U=1,V=1;
void dfs1(int u,int pre){
    if(dist1[u]>dist1[U]){
        U=u;
    }
    for(auto [v,w]:g[u]){
        if(v==pre) continue;
         dist1[v]=dist1[u]+w;
        dfs1(v,u);
       
    }
}
void dfs2(int u,int pre){
    if(dist2[u]>dist2[V]){
        V=u;
    }
    for(auto [v,w]:g[u]){
        if(v==pre) continue;
        dist2[v]=dist2[u]+w;
        dfs2(v,u);
        
    }
}
signed main(){
    cin>>n;
    for(int i=1;i<n;i++){
        int u,v,w;
        cin>>u>>v>>w;
        g[u].push_back({v,w});
        g[v].push_back({u,w});
    }
    dfs1(1,0);
    dfs2(U,0);
    cout<<dist2[V];
    return 0;
}