In this Kata, you will implement the [Luhn Algorithm](http://en.wikipedia.org/wiki/Luhn_algorithm), which is used to help validate credit card numbers.
Given a positive integer of up to 16 digits, return ```true``` if it is a valid credit card number, and ```false``` if it is not.
Here is the algorithm:
* Double every other digit, scanning **from right to left**, starting from the second digit (from the right).
  Another way to think about it is: if there are an **even** number of digits, double every other digit starting with the **first**; if there are an **odd** number of digits, double every other digit starting with the **second**:
  ```
  1714 ==> [1*, 7, 1*, 4] ==> [2, 7, 2, 4]
  12345 ==> [1, 2*, 3, 4*, 5] ==> [1, 4, 3, 8, 5]
  891 ==> [8, 9*, 1] ==> [8, 18, 1]
  ```
*  If a resulting number is greater than `9`, replace it with the sum of its own digits (which is the same as subtracting `9` from it):
  ```
  [8, 18*, 1] ==> [8, (1+8), 1] ==> [8, 9, 1]
  or:
  [8, 18*, 1] ==> [8, (18-9), 1] ==> [8, 9, 1]
  ```
* Sum all of the final digits:
  ```
  [8, 9, 1] ==> 8 + 9 + 1 = 18
  ```
* Finally, take that sum and divide it by `10`.  If the remainder equals zero, the original credit card number is valid.
    ```
    18 (modulus) 10 ==> 8 , which is not equal to 0, so this is not a valid credit card number
    ```
```if:fsharp,csharp
For F# and C# users:
The input will be a string of spaces and digits `0..9`
```
import numpy as np
def validate(cc_number):
    # split integer into array of digits
    arr = np.array([int(i) for i in str(cc_number)])
    # double every second digit from the right
    arr[-2::-2] *= 2
    # substract 9 from digits greater than 9
    arr[arr>9] -= 9
    # sum up all the digits and check the modulus 10
    return np.sum(arr) % 10 == 0
import numpy as np
def validate(cc_number):
    # split integer into array of digits
    arr = np.array([int(i) for i in str(cc_number)])
    # double every second digit from the right
    arr[-2::-2] *= 2
    # substract 9 from digits greater than 9
    arr[arr>9] -= 9
    # sum up all the digits and check the modulus 10
    return np.sum(arr) % 10 == 0