C几几

ll C(int a,int b)
{
	int i=0;
	double Cans=1;
	if(a==0)return 0;
	if(b==0)return 1;
	while(i<b){
		Cans*=(a-i);
		Cans/=i+1;
		i++;
	}
	return (ll)Cans;
}
/*
55为界 
求C几几 
20为界 
*/ 
ll C(int a,int b)
{
	int i=0;
	ll Cans=1;
	if(a==0)return 0;
	if(b==0)return 1;
	while(i<b){
		Cans*=(a-i);
		i++;
	}
	while(b){
		Cans/=b;
		b--;
	}
	return Cans;
}

C几几

原文：http://blog.csdn.net/qq_27803491/article/details/47790233