(Tree) Tree Diameter

#include <bits/stdc++.h>
using namespace std;
 
//#define int long long 
const long long  mod =1e9+7;
vector<vector<int> > adjList;
vector<bool> vis;
vector<int> parents;
int lastNode=1;

void bfs(int node){
    vis[node]=true;
    queue<int> q;
    q.push(node);

    while(!q.empty()){
        int curr=q.front();
        q.pop();
        for(int neighbor: adjList[curr]){
            if(!vis[neighbor]){
                vis[neighbor]=true;
                q.push(neighbor);
                parents[neighbor]=curr;
                lastNode=neighbor;
            }
        }
    }
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin>>n;
    adjList.resize(n+1);
    vis.resize(n+1, false);
    parents.resize(n+1, 0);
    for(int i=1; i<n; i++){
        int a, b;
        cin>>a>>b;
        adjList[a].push_back(b);
        adjList[b].push_back(a);
    }

    bfs(1);
    int lN=lastNode;
    for(int i=0; i<=n; i++){
        vis[i]=false;
    }
    bfs(lN);
    int fN=lastNode;
    int x=fN;
    int ans=0;
    while(x!=lN){
        x=parents[x];
        ans++;
    }
    cout<<ans<<endl;
    return 0;
}