BOJ 34088 It's a Mod, Mod, Mod, Mod World 2

void solve(){
    auto start = chrono::high_resolution_clock::now();

    bitset<32000> isPrime;
    isPrime.set();
    isPrime[0] = isPrime[1] = 0;
    rep(i, 2, 32000) if(isPrime[i]){
        for(ll j = (ll)i*i; j < 32000; j += i) isPrime[j] = 0;
    }
    vector<int> primes;
    rep(i, 2, 32000) if(isPrime[i]) primes.push_back(i);


    int N; cin >> N;
    vector<ll> A(N);
    rep(i, 0, N) cin >> A[i];

    int ans = (N+1)/2;
    while(1){
        auto end = chrono::high_resolution_clock::now();
        auto duration = chrono::duration_cast<chrono::milliseconds>(end - start);
        if(duration.count() > 900) break;
        int a = rand() % N, b = rand() % N;
        int diff = abs(A[a] - A[b]);
        vector<int> divs;
        for(int p: primes){
            if(p*p > diff) break;
            if(diff % p == 0){
                divs.push_back(p);
                while(diff % p == 0) diff /= p;
            }
        }
        if(diff > 1) divs.push_back(diff);
        for(int d: divs){
            map<int, int> mp;
            for(auto x: A) mp[x%d]++;
            for(auto [_, c]: mp) ans = max(ans, c);
        }
    }
    cout << ans;
}