n_choose_k

Ali Hamdi Ali Fadel · @AliOsm · about 3 years

def n_choose_k(n, k)
  raise ArgumentError.new 'K should be less than or equal to N' if k > n

  result = 1
  
  a = n - k + 1
  b = 1

  while a <= n do
    result = result * a / b
    a += 1
    b += 1
  end

  result

end