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369.cpp
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369.cpp
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#include <iostream>
using std::cout;
using std::cin;
using std::endl;
#include <cstdlib>
void initial(int *p,int n)
{
int i;
for (i=0;i<n;i++)
p[i]=i;
}
long long count(int key,int key1)
{
int i;
long long j;
int ture;
int f,d,k;
int *p;
int *q;
p=new int[key+1];
initial(p,key+1);
if (key-key1>key1) ture=key-key1,f=key1;
else ture=key1,f=key-key1;
q=new int[f+1];
initial(q,f+1);
d=f;
while (d!=0)
{
for (i=key;i>=ture+1;i--)
{
if (!(p[i]%q[d]))
{
p[i]/=q[d],q[d]=1;
break;
}
}
d--;
}
d=key;
while (d!=ture)
{
for (i=f;i>=1;i--)
if (q[i]%p[d]==0)
{
q[i]/=p[d],p[d]=1;
break;
}
d--;
}
d=f;
while (d!=0)
{
for (i=key;i>=ture+1;i--)
{
if (!(p[i]%q[d]))
{
p[i]/=q[d],q[d]=1;
break;
}
}
d--;
}
j=1;
for (i=ture+1;i<=key;i++)
j*=p[i];
for (i=1;i<=f;i++)
if (j%q[i]==0) j/=q[i],q[i]=1;
k=1;
for (i=1;i<=f;i++)
k*=q[i];
return j/k;
}
main()
{
int n,m;
while (cin>>n>>m && n || m)
cout<<n<<" things taken "<<m<<" at a time is "<<count(n,m)<<" exactly."<<endl;
return 0;
}