답안 #19882

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
19882	2016-02-25T06:37:03 Z	xdoju	팔찌 (kriii4_V)	C++14	6 / 100	16 ms	13724 KB

V

#include <cstdio>
#include <cmath>
#include <vector>
using namespace std;

const int MOD = 1000000007ll;

int modpow(int r, int n) {
	int ret = 1;
	while (n > 0) {
		if (n % 2 > 0) {
			ret = ((long long)ret * r) % MOD;
		}
		r = ((long long)r * r) % MOD;
		n /= 2;
	}
	return ret;
}

int modinv(int n) {
	return modpow(n, MOD - 2);
}

int modprod(int a, int b) {
	a = a % MOD;
	b = b % MOD;
	return ((long long)a * b) % MOD;
}

int modprod(int a, int b, int c) {
	c = c % MOD;
	return (modprod(a, b) * (long long)c) % MOD;
}

int moddiv(int a, int b) {
	return ((long long)a * modinv(b)) % MOD;
}

const int N = 1000000;
int lp[N + 1];
int phi[N + 1];
vector<int> pr;

void sieve() {
	phi[1] = 1;
	for (int i = 2; i <= N; ++i) {
		if (lp[i] == 0) {
			lp[i] = i;
			phi[i] = i - 1;
			pr.push_back(i);
		}
		else {
			if (lp[i] == lp[i / lp[i]]) {
				phi[i] = phi[i / lp[i]] * lp[i];
			}
			else {
				phi[i] = phi[i / lp[i]] * (lp[i] - 1);
			}
		}
		for (int j = 0; j < (int)pr.size() && pr[j] <= lp[i] && i * pr[j] <= N; ++j) {
			lp[i * pr[j]] = pr[j];
		}
	}
}

int geoseries(int k, int cnt) {
	if (k == 1) {
		return cnt;
	}

	int ret = (modpow(k, cnt) - 1 + MOD) % MOD;
	ret = modprod(ret, k);
	return moddiv(ret, k - 1);
}

int mpow[N + 1];

void proc() {
	sieve();

	int n, k;
	scanf("%d %d", &n, &k);

	for (int i = 1; i <= n; ++i) {
		mpow[i] = modpow(k, i);
	}

	int ssum = 0;
	for (int i = 1; i <= n; ++i) {
		int t = 0;

		int lmt = (int)(sqrt(i) + 0.00001);
		for (int p = 1; p <= lmt; ++p) {
			if (i % p != 0) {
				continue;
			}
			int q = i / p;

			t = (t + modprod(mpow[q], phi[p])) % MOD;
			if (p != q) {
				t = (t + modprod(mpow[p], phi[q])) % MOD;
			}
		}
		t = moddiv(t, i);
		ssum = (ssum + t) % MOD;
	}

	int ans = moddiv(ssum, 2);

	int x = moddiv(modprod(k + 1, geoseries(k, n / 2)), 4);
	int y = moddiv(geoseries(k, (n + 1) / 2), 2);

	printf("%d", (ans + 1 + x + y) % MOD);
}

int main() {
	//freopen("input.txt", "r", stdin);
	proc();
	return 0;
}

Subtask #1

6.0 / 6.0

#	결과	실행 시간	메모리	Grader output
1	Correct	15 ms	13724 KB	Output is correct
2	Correct	15 ms	13724 KB	Output is correct
3	Correct	15 ms	13724 KB	Output is correct
4	Correct	15 ms	13724 KB	Output is correct
5	Correct	15 ms	13724 KB	Output is correct
6	Correct	15 ms	13724 KB	Output is correct
7	Correct	15 ms	13724 KB	Output is correct
8	Correct	11 ms	13724 KB	Output is correct
9	Correct	11 ms	13724 KB	Output is correct
10	Correct	8 ms	13724 KB	Output is correct
11	Correct	11 ms	13724 KB	Output is correct
12	Correct	16 ms	13724 KB	Output is correct
13	Correct	15 ms	13724 KB	Output is correct
14	Correct	12 ms	13724 KB	Output is correct
15	Correct	15 ms	13724 KB	Output is correct
16	Correct	11 ms	13724 KB	Output is correct
17	Correct	15 ms	13724 KB	Output is correct
18	Correct	15 ms	13724 KB	Output is correct
19	Correct	15 ms	13724 KB	Output is correct
20	Correct	15 ms	13724 KB	Output is correct

Subtask #2

0.0 / 94.0

#	결과	실행 시간	메모리	Grader output
1	Correct	11 ms	13724 KB	Output is correct
2	Correct	15 ms	13724 KB	Output is correct
3	Incorrect	12 ms	13724 KB	Output isn't correct
4	Halted	0 ms	0 KB	-