【Luogu P7794】[COCI2014-2015#7] JANJE

[COCI2014-2015#7] JANJE：

题目大意：

题目有点长，链接。

思路：

简单组合题，初赛内容。

代码：

inline ll Read()
{
	ll x = 0, f = 1;
	char c = getchar();
	while (c != '-' && (c < '0' || c > '9')) c = getchar();
	if (c == '-') f = -f, c = getchar();
	while (c >= '0' && c <= '9') x = (x << 3) + (x << 1) + c - '0', c = getchar();
	return x * f;
}

int n, m;
ll c, x, y;
ll Ans[10] = {0, 1572864-6, 96, 24-6, 24576-6, 12, 6, 96, 1073741826ll-6};

int main()
{
	n = Read(), m = Read();
	if (m == 1) {puts("0"); return 0;}
	x = m * (m - 1) * (m - 2) / 6;
	x *= Ans[n];
	switch (n)
	{
		case 1: y = 2; break;
		case 3: y = 2; break;
		case 4: y = 2; break;
		case 8: y = 2; break;
		default: y = 0;
	}
	y *= m * (m - 1) / 2;
	printf ("%lld
", x + y);
	return 0;
}