code: public static int choose (int n, int k)
      {
          // Base case: One way to select or not select the whole set
          if (k <= 0 || k >= n) {
              return 1;
          }
  
          // Recurse using pascal's triangle
          return (choose(n-1, k-1) + choose(n-1, k));
      }
docs: Computes (N choose K), the number of ways to select K different elements from a set of size
  N.