Given an array of ones and zeroes, convert the equivalent binary value to an integer.
Eg: `[0, 0, 0, 1]` is treated as `0001` which is the binary representation of `1`.
Examples:
```
Testing: [0, 0, 0, 1] ==> 1
Testing: [0, 0, 1, 0] ==> 2
Testing: [0, 1, 0, 1] ==> 5
Testing: [1, 0, 0, 1] ==> 9
Testing: [0, 0, 1, 0] ==> 2
Testing: [0, 1, 1, 0] ==> 6
Testing: [1, 1, 1, 1] ==> 15
Testing: [1, 0, 1, 1] ==> 11
```
However, the arrays can have varying lengths, not just limited to `4`.
def binary_array_to_number(arr):
    return sum(digit * 2**i for i, digit in enumerate(reversed(arr)))
def binary_array_to_number(arr):
    return sum(digit * 2**i for i, digit in enumerate(reversed(arr)))