最も遠いノード

#include <iostream>
#include <string>
#include <vector>
#include <deque>
#include <algorithm>

using namespace std;

int solution(int n, vector<vector<int>> edge) {
    vector<int> graph[n+1];
    //int visit[20001];
    vector<int> visit(n+1, -1);
    
    for(int i=0; i<edge.size(); i++){
        graph[edge[i][0]].push_back(edge[i][1]);
        graph[edge[i][1]].push_back(edge[i][0]);
        visit.push_back(-1);
    }
    
    deque<int> q;
    q.push_back(1);
    
    visit[1] = 0;
    while(!q.empty()){
        int now = q.front();
        q.pop_front();
        
        for(int next : graph[now]){
            if(visit[next] == -1){
                visit[next] = visit[now] + 1;
                q.push_back(next);
            }
        }
    }
    
    int answer = 0;
    int max = *max_element(visit.begin(), visit.end());
    cout << max << endl;
    
    for(int i=1; i<n+1; i++){
        if(visit[i] == max){
            answer++;
        }
    }
    return answer;
}