답안 #19897

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
19897	2016-02-25T06:50:07 Z	xdoju	팔찌 (kriii4_V)	C++14	100 / 100	579 ms	21512 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;
}

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

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

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

inline 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;
	}
	if (cnt <= 0) {
		return 0;
	}

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

int mpow[N + 1];
long long psum[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);
	}

	for (int i = 1; i <= n; i++) {
		for (int j = i; j <= n; j += i) {
			int p = i;
			int q = j / i;
			psum[j] += modprod(mpow[q], phi[p]);
		}
	}

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

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

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

	int ans = moddiv(ssum % MOD, 2);

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

	ans = (ans + 1) % MOD;
	ans = (ans + x) % MOD;
	ans = (ans + y) % MOD;

	printf("%d", ans);
}

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

Subtask #1

6.0 / 6.0

#	결과	실행 시간	메모리	Grader output
1	Correct	12 ms	21512 KB	Output is correct
2	Correct	13 ms	21512 KB	Output is correct
3	Correct	16 ms	21512 KB	Output is correct
4	Correct	16 ms	21512 KB	Output is correct
5	Correct	16 ms	21512 KB	Output is correct
6	Correct	16 ms	21512 KB	Output is correct
7	Correct	16 ms	21512 KB	Output is correct
8	Correct	16 ms	21512 KB	Output is correct
9	Correct	16 ms	21512 KB	Output is correct
10	Correct	12 ms	21512 KB	Output is correct
11	Correct	16 ms	21512 KB	Output is correct
12	Correct	11 ms	21512 KB	Output is correct
13	Correct	16 ms	21512 KB	Output is correct
14	Correct	16 ms	21512 KB	Output is correct
15	Correct	15 ms	21512 KB	Output is correct
16	Correct	15 ms	21512 KB	Output is correct
17	Correct	17 ms	21512 KB	Output is correct
18	Correct	15 ms	21512 KB	Output is correct
19	Correct	16 ms	21512 KB	Output is correct
20	Correct	8 ms	21512 KB	Output is correct

Subtask #2

94.0 / 94.0

#	결과	실행 시간	메모리	Grader output
1	Correct	17 ms	21512 KB	Output is correct
2	Correct	16 ms	21512 KB	Output is correct
3	Correct	13 ms	21512 KB	Output is correct
4	Correct	43 ms	21512 KB	Output is correct
5	Correct	347 ms	21512 KB	Output is correct
6	Correct	420 ms	21512 KB	Output is correct
7	Correct	329 ms	21512 KB	Output is correct
8	Correct	404 ms	21512 KB	Output is correct
9	Correct	463 ms	21512 KB	Output is correct
10	Correct	544 ms	21512 KB	Output is correct
11	Correct	469 ms	21512 KB	Output is correct
12	Correct	522 ms	21512 KB	Output is correct
13	Correct	312 ms	21512 KB	Output is correct
14	Correct	507 ms	21512 KB	Output is correct
15	Correct	296 ms	21512 KB	Output is correct
16	Correct	352 ms	21512 KB	Output is correct
17	Correct	567 ms	21512 KB	Output is correct
18	Correct	328 ms	21512 KB	Output is correct
19	Correct	401 ms	21512 KB	Output is correct
20	Correct	579 ms	21512 KB	Output is correct