POJ 1942 Paths on a Grid (组合数学)

#include <iostream>
#include <string.h>
#include <math.h>
#include <queue>
#include <algorithm>
#include <stdlib.h>
#include <map>
#include <set>
#include <stdio.h>
using namespace std;
#define LL __int64
#define pi acos(-1.0)
const int mod=100000000;
const int INF=0x3f3f3f3f;
const double eqs=1e-8;
LL c(LL x, LL y)
{
int i;
double ans=1;
for(i=1;i<=x;i++){
ans*=(y-i+1)*1.0/i;
}
return (LL) (ans+0.5);
}
int main()
{
LL n, m;
while(scanf("%I64d%I64d",&n,&m)!=EOF&&n+m){
if(n>m) swap(n,m);
printf("%I64d\n",c(n,n+m));
}
return 0;
}