不容易系列之(4)——考新郎

#include <cstdio>

long long int m[30];

long long int C(int n, int m)
{
	long long int sum = 1, j = 1;
	for(int i = n; i >= n - m + 1; -- i)
	{
		sum = sum * i / j;
		j ++;
	}
	return sum;
}

long long int f(int n)
{
	m[2] = 1;
	m[3] = 2;
	
	for(int i = 4; i <= n; ++ i)
	{
		m[i] = (i - 1) * (m[i - 1] + m[i - 2]);
	}
	
	return m[n];
}

int main()
{
	int c, n, m;
	scanf("%d", &c);
	while(c --)
	{
		scanf("%d %d", &n, &m);
		printf("%lld\n", C(n, m) * f(m));
	}
	
	return 0;
}