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

 

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <cstdlib>

 4 #include <algorithm>

 5 

 6 #define LL long long int

 7 

 8 using namespace std;

 9 

10 int main()

11 {

12     double n, k;

13     int T;

14     scanf( "%d", &T );

15     while ( T-- )

16     {

17         scanf( "%lf%lf", &n, &k );

18         if ( n - k < k - 1 ) k = n - k + 1.0;

19         double ans = 1.0;

20         for ( double i = 1; i < k; ++i )

21         {

22             ans *= ( n - i ) / i;

23         }

24         printf( "%.0f\n", ans );

25     }

26     return 0;

27 }