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
", ans );
25     }
26     return 0;
27 }