##Task:
You have to write a function `add` which takes two binary numbers as strings and returns their sum as a string.
##Note:
* You are `not allowed to convert binary to decimal & vice versa`.
* The sum should contain `No leading zeroes`.
##Examples:
```
add('111','10'); => '1001'
add('1101','101'); => '10010'
add('1101','10111') => '100100'
```
def b2i(b):
    return sum(1 << i for i, x in enumerate(b[::-1]) if x == '1')

def add(a, b):
    return format(b2i(a) + b2i(b), 'b')
def b2i(b):
    return sum(1 << i for i, x in enumerate(b[::-1]) if x == '1')

def add(a, b):
    return format(b2i(a) + b2i(b), 'b')