2721.cpp

这些是我到目前在PKU上做出的题目

#include <stdio.h>

int a1,a2;
double c;

double ccc(int a,int b)
{
	double res;
	int i;
	res=1;
	if (b>a/2)
		b=a-b;
	for (i=a;i>=a-b+1;i--)
		res=res*i;
	for (i=b;i>=2;i--)
		res=res/i;
	return res;
}

int main()
{
	scanf("%d %d",&a1,&a2);
	while (a1!=-1)
	{
		c=ccc(a1+a2,a1)*ccc(26-a1-a2,13-a1)/ccc(26,13);
		if (a1!=a2)
			c=c*2;
		printf("%d-%d split: %.8f\n",a1,a2,c);
		scanf("%d %d",&a1,&a2);
	}
	return 0;
}