Jaden Studies Trees

    1#include <bits/stdc++.h>
    2using namespace std;
    3pair<int,int> bfs(int start, const vector<vector<int>> &g){
    4    int n = g.size() - 1;
    5    vector<int> dist(n + 1, -1);
    6    queue<int> q;
    7    dist[start] = 0; q.push(start);
    8    int far = start;
    9    while(!q.empty()){
    10        int u = q.front(); q.pop();
    11        if(dist[u] > dist[far]) far = u;
    12        for(int v : g[u]){
    13            if(dist[v] == -1){
    14                dist[v] = dist[u] + 1;
    15                q.push(v);
    16            }
    17        }
    18    }
    19    return {far, dist[far]};
    20}
    21int main(){
    22    ios::sync_with_stdio(0);
    23    cin.tie(0);
    24    int n; cin >> n;
    25    vector<vector<int>> g(n + 1);
    26    for(int i = 0; i < n - 1; i++){
    27        int u, v; cin >> u >> v;
    28        g[u].push_back(v);
    29        g[v].push_back(u);
    30    }
    31    if(n == 1){
    32        cout << 0 << "\n";
    33        return 0;
    34    }
    35    auto a = bfs(1, g);
    36    auto d = bfs(a.first, g);
    37    cout << d.second << "\n";
    38    return 0;
    39}
    40