Shared code

/* 777 */
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define FAST_IO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

vector<int> get_depth(int root,vector<vector<int>>&adj,int n){
    vector<int>depth(n,0);
    function<void(int,int)> dfs=[&](int node,int par){
        for(auto &child:adj[node]){
            if(child==par)continue;
            depth[child]=depth[node]+1;
            dfs(child,node);
        }
    };
    dfs(root,-1);
    return depth;
}

int get_diameter(vector<vector<int>>&adj,int n){
    int random=0;
    vector<int>depth;
    depth=get_depth(random,adj,n);
    int max_depth=-1,end_node=-1;
    for(int i=0;i<n;++i){
        if(depth[i]>max_depth){
            max_depth=depth[i];
            end_node=i;
        }
    }
    depth=get_depth(end_node,adj,n);
    int diameter=-1;
    for(auto &x:depth)diameter=max(diameter,x);
    return diameter;
}

void solve() {
    int n,u,v;cin>>n;
    vector<vector<int>>adj(n,vector<int>());
    for (int i = 1 ; i < n ; ++i) {
        cin>>u>>v;u--;v--;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    cout << get_diameter(adj,n);
}

int32_t main() {
    FAST_IO
    solve();
}