SPOJ 78 Marbles 组合数学

相当于从n-1个位置里面找k-1个位置放隔板

 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 #include <algorithm>

 #define LL long long int

 using namespace std;

 int main()
 {
     double n, k;
     int T;
     scanf( "%d", &T );
     while ( T-- )
     {
         scanf( "%lf%lf", &n, &k );
         if ( n - k < k -  ) k = n - k + 1.0;
         double ans = 1.0;
         for ( double i = ; i < k; ++i )
         {
             ans *= ( n - i ) / i;
         }
         printf( "%.0f\n", ans );
     }
     return ;
 }