题解 | #幸运数字Ⅱ# 一定要对所有数字开longlong

queue <ll> ads;
queue <ll> ads1;
vector<ll> sav;
ll l, r;
//广搜构造幸运数字表
void dfs(ll n)
{
	ads.push(0);
	ll a;
	ll b;
	do {
		for ( int i = 4; i <= 7; i += 3 )
		{
			a = ads.front() * 10 + 4;
			b = ads.front() * 10 + 7;
			ads.push(a);
			ads.push(b);
			sav.push_back(a);
			sav.push_back(b);
			ads.pop();
		}
	} while ( ads.front() < r );
}

int main(int arg, char** argv) {
	/*ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin.tie(nullptr);*/
	cin >> l >> r;
	dfs(0);
	sort(sav.begin(), sav.end());
	auto t1 = lower_bound(sav.begin(), sav.end(), l) - sav.begin();
	auto t2 = lower_bound(sav.begin(), sav.end(), r) - sav.begin();
	ll sum{};
    //sum必须是ll，如果是double输出就是指数输出了
	/*cus::print(sav);
	coute;*/
// 	cout << t1 << " " << t2 << endl;
	for ( ll i = t1; i <= t2; i++ )
	{
		sum += (min(sav[i], r) - l + 1) * sav[i];
		l = sav[i] + 1;
	}
	cout << sum;
	return 0;
}