cartog.cpp

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>

#define MAX 1000000

using namespace std;

vector<int> grafo[MAX];
int n, vis[MAX], d_max = -1;

void bfs(int vert_ini) {
    int d[n];
    memset(d, 0, sizeof d);

    queue<int> fila;
    fila.push(vert_ini);

    d[vert_ini] = 0;
    while(!fila.empty()) {
        int v = fila.front();
        fila.pop();

        vis[v] = 1;
        for(int j = 0; j < n; j++)
            if((find(grafo[v].begin(), grafo[v].end(), j) != grafo[v].end()) && v != j && vis[j] == 0) {
                fila.push(j);
                vis[j] = 1;
                d[j] = d[v] + 1;

                if(d[j] > d_max)
                    d_max = d[j];
            }
    }
}

int main() {

    memset(vis, 0, sizeof vis);

    cin >> n;

    for(int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;

        a--, b--;

        grafo[a].push_back(b);
        grafo[b].push_back(a);
    }

    for(int i = 0; i < n; i++)
        bfs(i);

    cout << d_max << endl;

    return 0;
}