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input/code.cpp: In function 'int main()':
input/code.cpp:56:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int a = 0; a < round_max; ++a) {
                    ~~^~~~~~~~~~~

#include <iostream>
#include <unordered_map>
#include <vector>

using namespace std;

vector<int> gen_primes(int n) {
	vector<int> result = {2};
	for (int i = 3; i*i <= n; ++i) {
		bool good = true;
		for (auto p : result) {
			if (i % p == 0) {
				good = false;
				break;
			}
		}
		if (good) result.push_back(i);
	}
	return result;
}

vector<int> prime_facts(int x, const vector<int> &primes) {
	vector<int> result;
	for (auto p : primes) {
		if (p > x) break;
		if (x % p == 0) {
			result.push_back(p);
			do {
				x /= p;
			} while (x % p == 0);
		}
	}
	if (x > 1) result.push_back(x);
	return result;
}

int main()
{
	int n;
	cin >> n;
	vector<int> nums(n);
	int maximum = 0;
	for (int i = 0; i < n; ++i) {
		cin >> nums[i];
		maximum = max(maximum, nums[i]);
	}
	auto primes = gen_primes(maximum);
	unordered_map<int, int> counts;
	unordered_map<int, int> parity;
	long long ans = n * (n - 1) / 2;
	for (int i = 0; i < n; ++i) {
		auto facts = prime_facts(nums[i], primes);
		vector<pair<int, int>> products = {{0, 1}};
		for (auto f : facts) {
			auto round_max = products.size();
			for (int a = 0; a < round_max; ++a) {
				auto new_count = products[a].first + 1;
				auto new_product = products[a].second * f;
				++counts[new_product];
				parity[new_product] = new_count % 2;
				products.push_back({new_count, new_product});
			}
		}
		//cout << i << endl;
		//for (auto p : products) {
		//	cout << p.first << " " << p.second << endl;
		//}
	}
	//cout << "---" << endl;
	for (auto x : counts) {
		//cout << x.first << " " << x.second << " " << parity[x.first] << endl;
		//cout << x.second * (x.second - 1) / 2 << endl;
		if (parity[x.first] == 1) {
			ans -= (long long)x.second * ((long long)x.second - 1) / 2;
		} else {
			ans += (long long)x.second * ((long long)x.second - 1) / 2;
		}
	}
	cout << ans << endl;
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 2, 3

Verdict: WRONG ANSWER

Test 4

Group: 3

Verdict: WRONG ANSWER

Test 5

Group: 3

Verdict: WRONG ANSWER

Test 6

Group: 3

Verdict: WRONG ANSWER

Test 7

Group: 3

Verdict: WRONG ANSWER