Submission #1129703

#	Time	Username	Problem	Language	Result	Execution time	Memory
1129703		antonn	Asceticism (JOI18_asceticism)	C++20	100 / 100	10 ms	1352 KiB

asceticism

// https://oeis.org/A008292
#include <bits/stdc++.h>
using namespace std;

const int Nmax = (1 << 17);
const int Mod = 1e9 + 7;

int Fact[Nmax], IFact[Nmax];

int mul(int a, int b) {
    return 1LL * a * b % Mod;
}

int pow(int a, int b) {
    int res = 1;
    while (b > 0) {
        if (b & 1) res = mul(res, a);
        a = mul(a, a);
        b >>= 1;
    }
    return res;
}

int binom(int n, int k) {
    if (n < k) return 0;
    return mul(Fact[n], mul(IFact[k], IFact[n - k]));
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    
    Fact[0] = 1;
    for (int i = 1; i < Nmax; i++) Fact[i] = mul(Fact[i - 1], i);
    IFact[Nmax - 1] = pow(Fact[Nmax - 1], Mod - 2); 
    for (int i = Nmax - 2; i >= 0; i--) IFact[i] = mul(IFact[i + 1], i + 1);
    
    int N, K; cin >> N >> K;
    int answer = 0;
    for (int i = 0; i <= K; i++) {
        int coef = mul(pow(K - i, N), binom(N + 1, i)) % Mod;
        if (i % 2 == 0) {
            answer += coef;
            if (answer >= Mod) answer -= Mod;
        }
        if (i % 2 == 1) {
            answer -= coef;
            if (answer < 0) answer += Mod;
        }
    }
    cout << answer << "\n";
    return 0;
}

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 51 / 51