POJ-1942-Paths on a Grid-组合水题

http://poj.org/problem?id=1942
求C(n+m,n)
这题数据有点特殊....

C（a,b）的b 取min(b,a-b)就能ac了。。。

求组合只能实打实边乘边除了。。用ll或double足矣

#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <stack>
#include <iostream>
using namespace std;  
__int64 inf=15;
double eps=0.000001;    

__int64 C(__int64 a,__int64 b)
{
	__int64 ans=1;
	if (b<a-b) b=a-b;
	__int64 i;  
	__int64 tmp=a-b;
	for (i=a;i>b;i--)
	{
		ans*=i;
		while(tmp>1&& ans%tmp==0 )
		{ans/=tmp;tmp--;}
	}

return ans;
}
int main() 
{ 
	__int64 n,m;
	while(scanf("%I64d%I64d",&n,&m)!=EOF)
	{
		if (!n&&!m) break;
		__int64 ans=1;
		__int64 tmp=n+m; 
		ans=C(tmp,n);  
		printf("%I64d\n",ans);
	}
	
	return 0;
}

double：

#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <stack>
#include <iostream>
using namespace std;  
__int64 inf=15;
double eps=0.000001;    

__int64 C(__int64 a,__int64 b)
{
	double  ans=1;
	if (b<a-b) b=a-b;
	__int64 i;  
	__int64 tmp=a-b;
	for (i=a;i>b;i--)
	{
		ans*=i;
		while(tmp>1&& (__int64)(ans)%tmp==0 )
		{ ans=ans/ (double)tmp;
		ans=(__int64)(ans+0.5);tmp--;}
	}
	
	return (__int64)(ans+0.5);
}
int main() 
{ 
	__int64 n,m;
	while(scanf("%I64d%I64d",&n,&m)!=EOF)
	{
		if (!n&&!m) break;
		__int64 ans=1;
		__int64 tmp=n+m; 
		ans=C(tmp,n);  
		printf("%I64d\n",ans);
	}
	
	return 0;
}