Submission #1245284

#	Time	Username	Problem	Language	Result	Execution time	Memory
1245284		kchu_z	Rack (eJOI19_rack)	C++20	100 / 100	0 ms	328 KiB

rack

#include <bits/stdc++.h>
using namespace std;

const unsigned long long MOD = 1e9 + 7;

unsigned long long power(unsigned long long exp) {
    if (exp == 0) return 1;
    if (exp % 2 == 0) {
        unsigned long long x = power(exp / 2);
        return (x * x) % MOD;
    }

    return (2 * power(exp - 1)) % MOD;
}

int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    unsigned long long n, k, s = 0;
    cin >> n >> k;
    k--;

    for (unsigned long long mask = 0; mask < 64; mask++) {
        if (k & (1LL << mask)) s = (s + power(n - 1 - mask)) % MOD;
    }

    cout << (s + 1) % MOD << endl;
    return 0;

}

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