https://programmers.co.kr/learn/courses/30/lessons/12977

void BT(vector<int>& nums, int index, int count, int sum, int& answer) {
	if (count == 3) {
		bool flag = true;
		for (int i = 2; i * i <= sum; i++) {
			if (sum % i == 0)
			{
				flag = false;
				break;
			}
		}
		if (flag == true) answer++;
		return;
	}
	for (int i = index; i < nums.size(); i++) {
 		BT(nums, i + 1, count + 1, sum + nums[i], answer);
	}
}

int solution(vector<int> nums) {
	int answer = 0;
	BT(nums, 0, 0, 0, answer);
	return answer;
}