Generating a tree

#include "bits/stdc++.h"
using namespace std;

#define int long long

inline int rand(int l, int r){
    static std::mt19937 rng(std::chrono::steady_clock::now().time_since_epoch().count());
    std::uniform_int_distribution<int> uid(l, r); return uid(rng);
}
const int N = 1e5+4;
#define rep(i,a,n) for (int i = a; i <= n; ++i)

int parent[N];

int find(int x) {
    if (x == parent[x]) {
        return x;
    }
    return parent[x] = find(parent[parent[x]]);
}

void join(int x, int y) {
    int px = find(x);
    int py = find(y);
    parent[px] = py;
}

signed main() {
    int n = rand(1, 10);
    rep(i,1,n)
        parent[i] = i;
    cout << "1\n" << n << '\n';
    vector < pair < int, int > > v;
    rep(i,1,n)
        rep(j,i+1,n)
            v.push_back({i, j});
    random_shuffle(v.begin(), v.end());
    int cnt = 0;
    for (auto i : v) {
        if (find(i.first) != find(i.second)) {
            join(i.first, i.second);
            ++cnt;
            cout << i.first << ' ' << i.second << ' ' << rand(1, n) << '\n';
        }
        if (cnt == n-1)
            break;
    }
}