Submission #19960

#	Time	Username	Problem	Language	Result	Execution time	Memory
19960		gs13068	순열 (kriii4_T)	C++98	100 / 100	367 ms	8896 KiB

T

#include <cstdio>
#include <algorithm>

const int p = 1000000007;

using namespace std;

int f(int x, int y)
{
	return y & 1 ? (long long)f(x, y ^ 1)*x%p : y ? f((long long)x*x%p, y >> 1) : 1;
}

int fac[1000001];
int inv[1000001];

int main()
{
	int i, j, n, m, r = 0;
	scanf("%d%d", &n, &m);
	fac[0] = 1;
	for (i = 1; i <= n + 1; i++) fac[i] = (long long)fac[i - 1] * i % p;
	inv[n + 1] = f(fac[n + 1], p - 2);
	for (i = n + 1; i >= 1; i--) inv[i - 1] = (long long)inv[i] * i % p;
	for (i = 0; i < n - m; i++)
	{
		j = fac[n - i];
		j = (long long)j * fac[n - m + 1] % p;
		j = (long long)j * inv[n - m - i - 1] % p;
		j = (long long)j * f(i + 2, p - 2) % p;
		r = (r + j) % p;
	}
	printf("%d", r);
}

• Subtask 1: 8 / 8
• Subtask 2: 92 / 92