Submission #237671

#	Time	Username	Problem	Language	Result	Execution time	Memory
237671		RiscadoA	Rack (eJOI19_rack)	C++14	100 / 100	6 ms	384 KiB

rack

#include <bits/stdc++.h>

using namespace std;

const int64_t MOD = 1000000007;

int64_t fast_pow(int64_t x, int64_t y) {
    x %= MOD;
    if (x == 0) {
        return 0;
    }

    int64_t res = 1;
    while (y > 0) {
        if (y % 2 == 1) {
            res = (res * x) % MOD;
        }

        y >>= 1;
        x = (x * x) % MOD;
    }

    return res;
}

int64_t solve(int64_t n, int64_t k) {
    if (n == 0) {
        if (k != 0) {
            abort();
        }

        return 1;
    }

    if (k % 2 == 0) {
        return solve(n - 1, k / 2);
    } else {
        int64_t k2 = 0;
        if (k > 1) {
            k2 = k / 2;
        }
        
        return (fast_pow(2, n - 1) + solve(n - 1, k2)) % MOD;
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int64_t n, k;
    cin >> n >> k;
    cout << solve(n, k - 1) << endl;
}

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