チャレンジ

#include <bits/stdc++.h>
using namespace std;
mt19937 rng(167);
int rand_int(int l,int r){
    return uniform_int_distribution<int>(l, r)(rng);
}

int main(){
    const int MAX_N = 200'000;
    const int MIN_A = 1;
    const int MAX_A = 1'000'000'000;
    vector<int> A;
    while ((int)A.size() != MAX_N){
        int a = rand_int(MIN_A, MAX_A);
        int c = rand_int(2, 10);
        c = min(c, (int)(MAX_N - A.size()));
        while (c--) A.push_back(a);
    }
    cout << A.size() << endl;
    for (int i = 0; i < (int)A.size(); i++){
        cout << A[i] << (i + 1 == (int)A.size() ? "\n" : " ");
    }
}