Submission #466234

#	Time	Username	Problem	Language	Result	Execution time	Memory
466234		Stickfish	Rack (eJOI19_rack)	C++17	100 / 100	1 ms	204 KiB

rack

#include <iostream>
#include <vector>
using namespace std;
using ll = long long;

const ll MOD = 1e9 + 7;

ll pw(ll a, ll m){
	if(!m)
		return 1;
	a %= MOD;
	if(m % 2)
		return (a * pw(a, m - 1)) % MOD;
	return pw(a * a, m / 2);
}

signed main(){
	ll n, k;
	cin >> n >> k;
	--k;
	ll ans = 0;
	ll r2 = pw(2, MOD - 2);
	ll pw2 = pw(2, n - 1);
	for(ll i = 0; i < min(n, 63ll); ++i){
		if(k & (1ll << i)){
			ans += pw2;
			ans %= MOD;
		}
		pw2 = (pw2 * r2) % MOD;
	}
	cout << ans + 1 << endl;
	//if(n <= 20){
		//vector<ll> a = {1};
		//for(int sz = 1, pw = (1 << (n - 1)); sz <= k; sz *= 2, pw /= 2){
			//for(int i = 0; i < sz; ++i){
				//a.push_back(a[i] + pw);	
			//}
		//}
		//cout << a[k] << endl;
	//}
}

• Subtask 1: 20 / 20
• Subtask 2: 20 / 20
• Subtask 3: 60 / 60